Timber structures

Ekaterina Rovnova

TIMBER STRUCTURES

Component name: Digital notebook Module Name: Technologies for Architecture and Urbanism

Moscow MARCH 2014

TABLE OF CONTENTS

Preface 05 Bridges Achieving Safety 08 Timber Bridges 14 Aultnaslanach Viaduct 16 Traversina Bridge 18 Murau Bridge 24 Moveable Bridges 28 Footbridge in Duisburg 32 Rolling Bridge in London 34 Surfaces Forces in Structures 38 Canopy design proposal 40

Timber Hyperbolic Structures Multi-purpose hall in Leuk 44 Leisure Pool in Freiburg 45

Review of types of structures and detailing 46

Supersam Market in Warsaw 50 Folded-Plate Structures 52

The Material Species of wood 56 Wood-based products 58 Timber towers Stadthaus 64 FortĂŠ house 68 Bridport house 70

Future of timber Multi-storey buildinigs Types 74 Construction Sequence 78 Examples 82 Enviroment Environmental impacts 86 Carbon Cycle 87 Carbon footprinting 88 References 91

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PREFACE

BRIDGES How to achieve safety? How to span the hundreds of metres?

How technical drawings and theoretical basis are implemented in real life? How to make bridge to move? What are the main principles of moveable bridges? What kinds of mechanism could be used in such cases?

SURFACES How to span the hundreds of metres, how to make staying under such structure safety and pleasant? How to achieve great design in detailing?

THE MATERIAL What wood species are used and in what kinds of production?

What is better for furniture and what is better for high stress structures? What wood-based products do exist? What are their properties and field of application?

TIMBER TOWERS Is it possible to erect multi-storey building completely from timber? What height is maximum for such structures? How high is the tallest wooden residential building? What are the future trends? Is it profitable to build timber high rises?

ENVIRONMENT What is about sustainability? How do timber building impact on environment? Is it really better to use wood instead of concrete or steel? What are advantages and drawbacks?

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BRIDGES

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SELECTING AND CONFIGURING STRUCTURAL SYSTEM TO ACHIEVE SAFETY AND SERVICEABILITY

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BRIDGES

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010

BRIDGES

Treetop Catwalk Proposal 21. 10. 2013

A design for a footbridge with non-coaxial timber pylons First ideas

011

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BRIDGES

I was hesitating if such structure needs an additional support. But in order to resist lateral forces presence of the steel cables is appropriate

wooden uprights steel truss

Another parabolic example of a truss system (but the timber one) is shown on the p.17

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TIMBER BRIGES

Principles of use of wood in bridges In engineering structures, the materials are not adapted to all types of stress: concrete is well adapted to parts working in compression, steel with parts working in tension. Although the performance of healthy wood in bending and axial tension is very satisfactory, bending will be limited by the sliding forces on supports (longitudinal shear between fibers) and the axial tensile stresses are limited by the nature of the joints that produce localized shear stresses. Moreover, even if the healthy wood has good performance in tension, wood with singularities such as knots, loses part of its characteristics in tension.

For wood, the optimum is thus to make the material work in axial compression, preferably in full section. This brings in arch type load bearing systems, beams under braces or lattices. As only round or rectangular wood sections are available industrially, contrary to steel which allows the manufacture of I-sections with good bending properties, timber beams in general do not have optimized bending properties hence the need for supports, and the possible spans are rather modest.

How to associate wood and other materials The association of materials having different and complementary properties makes it possible to improve operation of the structures, by using each material in its preferred field.

Concrete has a good compressive strength, but a low tensile strength. It can be associated with wood as a collaborating compressed slab, which will allow removal of shear stresses harmful to bending in wood alone and can also ensure protection of the wood frame from bad weather. The wood-concrete joint must ensure a sufficiently rigid connection between the timber beams and thereinforced concrete slab in order to use these materials to their full capacity.

Steel has excellent tensile characteristics but is limited in compression because of the phenomena of buckling. The association of tensioned steel and compressed wood will make it possible to lengthen the spans. It will be necessary to give a light camber to the timber part to avoid any excessive deformation after creep.

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BRIDGES

BRACKLINN FALLS FOOTBRIDGE This bridge represents a simple structural form. Four 12m long Douglas Fir trunks form the main structural members in an A-frame truss arrangement. The central part of the bridge is roofed in copper sheeting, which helps obscure the presence of steel bracing at the truss crown.

The bridge was installed by winching it across on greased metal tracks supported on a temporary timber structure.

The load from the bridge is carried by the massive main timbers, but their thrust is restrained by curved tie members below the deck. These are steel plates, two on each edge of the bridge, and shaped with a gentle scalloping between points of connection.

DUTTON HORSE BRIDGE This twin-span timber bridge was completed in 1919 to a design by John Saner. It is historically significant as one of the earliest surviving bridges to feature laminated timber.

The laminated arches span about 31m, with two ribs slightly out of line with each other. Each span consists of paired semi-elliptical timber arches of mechanically laminated timber, strengthened with triangulated timber struts, which also support the deck. The paired arches are braced by cast-iron struts. The bridge platform is 2.4 m wide with a gentle arch. It has simple timber guard rails of the post-and-rail type. The deck was originally constructed of asphalt-coated timber slats. The central pier rests on two connected cylindrical columns of concrete-filled brick.

KINTAI BRIDGE The bridge was built in 1673, spanning the Nishiki River in a series of five wooden arches.The bridge is composed of five sequential wooden arch bridges on four stone piers as well as two of wooden piers on the dry riverbed where the bridge begins and ends. Each of the three middle spans is 35.1 meters long, while the two end spans are 34.8 meters for a total length of about 175 meters with a width of 5 meters. For nearly three hundred years, bridge stood without the use of metal nails. This was achieved by the careful fitting of the wooden parts and by the construction of the thick girders by clamping and binding them together with metal belts. The main wooden parts of the bridge were covered by sheets of copper for additional durability

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AULTNASLANACH VIADUCT

Completed 1897. This is the last timber viaduct existing on a main line Scottish railway, a rare and substantial survivor of a once fairly common bridge type.

The bridge is 40.41m in length by 8.69m in width with raking shores spreading the width to 18.29m overall. There are five spans, varying between 7.42m and 7.65m in length centre to centre, and the decking stands 8.46m above the normal water-line of the burn.

The sectional corrugated-iron deck is carried on a series of six longitudinal girders, each made up of coupled baulks mounted on top of the other. There are six trestle bents, the two end ones being set within the embankments. Each of the four central frames is composed of six upright posts driven into the ground like piles and joined together by runners, beam-stiffeners and, at the head, a transverse beam. The main structural components are braced laterally by raking shores, and longitudinally by an elaborate system of raking struts associated with the main girders and a lower straining-beam.

View of Aultnaslanach Viaduct, from north west, showing half-elevation and section through centre-bay 16

BRIDGES

This is a rare example of complete timber structure without association with any other materials

Details of the structural frame

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BRIDGE OVER THE TRAVERSINER TOBEL

The cable stayed bridge spans 56 meters, about 80 meter above the valley, and it connects places with a height difference of 22 meter. It’s not only a bridge, but a staircase. The the bridge deck hangs from steel cables. Its funicular, together with the steep stair, give rise to a powerful structure.

The two main steel cables, of just 36 mm of diameter, carry the load by means of tension to the foundations located in both sides of the river. Hanging from them, smaller cables (10 mm of diameter) hold the glue-laminated larch beams. The secondary cables are attached to I-section cross steel beams, and the wood beams are set above them.

(2)

(1)

(3) the inclined bridge deck pulls from the upper support the inclined bridge deck pushes on the lower support

The bridge’s own weight (26 tons) is trying to drag the foundation into the river, and inclined bridge deck pulls from the upper supports. The weight of the foundation is the only tool to stand the forces leading to crash, so the foundation of this apparently light bridge weighs seven (!) times more (192 tons) than the bridge itself.

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BRIDGES

(4)

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(1) junction of the main cable and secondary cables

(2) junction of the secondary cables

A robust wind-bracing system is created by diagonal rods and ten parallel timber beams, mounted on the cross-beams, that form the lower compressed chord.

Two longitudinal beams (4) situated outside the line of the footpath increase the sense of security for hikers, preventing a direct view down into the 70-metre-deep gorge.

Durability and weather resistance were achieved by using materials such as larch and hot-dip galvanized steel, and by minimizing horizontal areas and the surface contact between elements.

Construction sequence algorithm

(3) upper bridge support

And how this algorithm was implemented 20

BRIDGES

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TRAVERSINA BRIDGE

1996-1999 J端rg Conzett

Forming part of a scheme to make the spectacular scenery of this area more accessible, the bridge was designed to be flown in by helicopter. This restricted the maximum transport weight to 4.3 tonnes. The load-bearing system comprises two elements: a lightweight parabolic beam structure, trussed on the underside and with a timber compression chord; and the balustrade beams, consisting of sandwich sheets, which resist torsion. The two elements were connected by H-shaped balustrade frames, the legs of which extend vertically downwards. A laminated larch bracing member was fixed above the compression chord. The paving was in tongued-and-grooved boarding. The bridge was destroyed by an avalanche in March 1999

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BRIDGES

The bridge is made of larch wood and non-corrosive steel cables. The structure consists of a parabolic truss system wherethe triangular trusses get smaller on the ends, causing the two cables at each of the bottom vertices of the triangle to curve in a parabola.

There are 23 struts created by triangles. The triangle trusses are connected to the girder where each one is pinned down by five cables.

A key design constraint was the need to replace any single piece of the structure without a need for auxiliary support. In this way, the structure could be maintained indefinitely using locally grown timber. This explicit design goal helped to achieve an elegant structure with low life cycle costs and improved environmental performance.

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MURAU BRIDGE

The footbridge connects four different starting points at just as many different levels. The actual junction is a post-tensioned timber girder with a large free span that connects the railway directly with the town.

Various access ways open up, each with its own arm, like splitoff pieces of the timber girder lying scattered on the ground.

The wood construction of the load-bearing structure is treated as a monolithic body whose lower and upper flange reinforcements carry the roof and floor of the bridge. In immediate proximity to the engineer’s load-bearing structure plan, the actual bridge space is created through manipulation of its static elements: slabs and plates.

In this, the core of the idea was shaped by the single-span Vierendeel girder. This novel construction in wood provided the base for the spatial interpretation of the footbridge.

construction axonometry with dismantled shear walls 24

BRIDGES

The Vierendeel girder allows a huge window to open precisely at the site of the greatest bending moments in the middle of the river. There, the four entry spaces, which are separated by shear walls, merge to the central space of the bridge.

The sideways shifted shear walls align with the horizontal surfaces of the floor and the roof of the space through their diagonal placement. Truly innovative about this bridge was the integrated construction, developed together with Jurg Conzett and Kaufmann Holzbau in Vorarlberg. The prestressing of the lower flange as well as the production of very large, timber carrying parts presented challenges. glue-laminated upper chord

view shear wall

prefabricated parapet element

glue-laminated lower chord

channel for post-tensioning cable

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view from the city side

cross section of bridge with footbridge strain isometry of the main support

In this bridge, the principle of glueing and pressing arises in different scales: first by the industrialized process of forming glue-laminated timber beams out of wooden boards. As many as five of these beams are assembled by glueing within a pneumatic compression press to the lower and upper chords: for the shear walls, they are pressed by a dense nailing.

Finally, the chords were delivered to the building site in two pieces each and glued with an epoxy resin. There, the necessary pressure was applied by the structure’s dead weight (upper chord) or by a post-tensioned cable of 409 tons (lower chord). This procedure enabled the production of a wooden bridge as a spatial system solely from the structural parts.

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BRIDGES bending moments and the course of the lateral force in the main support

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Openable Bridge Design Proposal The next task was to design a footbridge linking two footpaths over the navigable channel, so this bridge should be openable. My solutions were rather poor, because of the lack of the time and the lack of experience: frankly speaking, I have never seen any moveable bridges excepting simple bascule ones.

cables mounted on the bridge deck should turn around beams between two main bearing arches

rolling mechanism is hidden here, between bearing arches and below bridge deck

in sliding variant hidden mechanism should also turn cables mounted to the moving parts of a bridge deck; thus the bridge opens

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BRIDGES

Cable-stayed bridge variant with the same opening mechanism

Later I found one appropriate example that perfectly fits my idea: it is a moveable suspension bridge in Duisburg (pp.31-32)

the next mad idea, why don’t to pull openable part down? In that case rolling mechanism should always be in operation condition keeping cables in tension, so it is a failed decision

The only one depressing conclusion is that my architectural thought was paralysed by clumsy attempts to invent some opening mechanism. Ultimately I had neither good design, nor good engineering idea.

Much more inspiring examples of moveable bridges are represented on the next pages 29

MOVEABLE BRIDGES

a drawbridge* hinged on pins with a counterweight to facilitate raising

a drawbridge with multiple sections that collapse together horizontally

the bridge deck is lifted by counterweighted cables mounted on towers

a lift bridge with the lifting mechanism mounted underneath it

the bridge deck is retracted to one side

an unhinged drawbridge lifted by the rolling of a large gear segment along a horizontal rack

also called a ducking bridge, the bridge deck is lowered down into the water

the bridge deck rotates around a fixed point, usually at the centre, but may resemble a gate in its operation

the bridge deck, which is curved and pivoted at each end, is lifted at an angle

a structure high above carries a suspended, ferry-like structure

a drawbridge with multiple sections that curl vertically

*drawbridge - the bridge deck is hinged on one end

EXAMPLES OF MOVEABLE BRIDGES

STALHILLE FOOTBRIDGE A permanent mobile pedestrian bridge with a 26m span and 3m wide on the same site.

The basic kinematic idea behind this innovation is to keep the same static system for the simply supported bridge beam in all three positions: closed, moving and open. The 20-ton bridge beam is suspended from four arms that can rotate around their central point – the point of rotation.

At the other extremities of the arms, four steel counterweights balance the movement of the bridge beam. A hydraulic system incorporated into the supporting portal frames uses the weight difference between the bridge beam and the counterweights to control the bridge’s swinging around the point of rotation.

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BRIDGES

FOLDABLE BRIDGE IN KIEL A folding mechanism, developed without any hidden dynamics, enables ships to pass through. At the points marking its thirds, the folding part of the deck is subdivided by hinges. The deck is borne on both sides by two cables that are deviated via two mast portals and are anchored in the foundation of the jetty.

One mast portal is connected rigidly with the deck, both portals have hinged joints at their bases. In this way, not only does an eye-catching movement unfold, but the surface area exposed to wind is also reduced. In all positions and under all loads the cable system is statically determinate. The primary framework construction and lateral disc elements ensure structural stability.

GATESHEAD MILLENNIUM BRIDGE It is a cable-stayed tilt bridge (the world’s first rotating bridge). The steel arch supports the curved steel deck using 18 steel cables. Tilt bridge is essentially made up of two curves, which pivot around their common springing points to allow ships to pass underneath. The second deck counterbalances the other. The top of the arch reaches 50 metres above the water and forms an arc over the river.

When ships needs to pass through, the bridge opens hydraulically by tilting dramatically upwards from the surface of the water – quite a sight. The eight engines that drive it are housed in glass canopies at each end of the bridge. Opening and closing takes four and half minutes.

SAMUEL BECKETT BRIDGE Cable-stayed swing bridge. Its deck is suspended on 31 cables (6 at the back, 25 at the front) and swings through 90 degrees to let ships pass. The bridge is 123 m long, 33 m wide at its widest point and 45 m high to the top of the pylon.

It is shaped like a harp, the Irish emblem, on its side, and was designed by Santiago Calatrava. The pylon is an impressive piece of work: 120 mm thick steel plates shaped in different forms and directions to establish the arched effect. The turning point of this swing bridge is not in the centre and therefore the bridge has to be ballasted with a weight of 2800 tonnes of concrete and steel.

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FOOTBRIDGE OVER THE INNER HARBOUR DUISBURG

A movable back-anchored suspension bridge is 3.5 m wide with a span about 73 m. Because of ship traffic in the harbour, the deck has to be raised to a clearance of 10.6 m above high water level.

To allow this, the back stays can be shortened by hydraulic cylinder jacks by 3 m. Thus the masts pivot outwards, and the deck, consisting of precast concrete elements is automatically lifted upwards into an arched shape.

To permit the bridge deck’s curvature during lifting, the deck elements are joined by hinges. The additional length of the walkway is provided by one additional deck element on either side which can be pulled out from pockets in the abutment.

The maximum longitudinal slope in «open» state is 45 degrees. Theoretically, (and it is really useful feature) the bridge could still be used at that stage, but it is recommended to leave the bridge beforehand.

20 m

73 m

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BRIDGES

hydraulic cylinder jack

hydraulic cylinder jack basement

mounting of the steel cable to the deck slab

This design develops my proposal for a moveable pedestrian bridge: if the bridge deck were divided into two parts, it could be like bascule suspension bridge that is represented on pp.26-27.

Certainly, this one is better than mine 33

ROLLING BRIDGE IN LONDON

This pedestrian bridge spans a canal of 8.1 m in width. The bridge needed to open to allow access for the boat moored in the inlet. Rolling Bridge opens by slowly and smoothly curling until it transforms from a conventional, straight bridge, into a octagon sculpture which sits on the bank of the canal.

The structure opens using a series of hydraulic rams integrated into the balustrade. As it curls, each of its eight segments simultaneously lifts, causing it to roll. The bridge can be stopped at any point along its journey.

It is said that studio’s aim was to make function from movement. As such it can be stopped at any point, whether at the very start, when it looks as though it is hovering, or halfway through its opening path.

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BRIDGES

pin bushing

pinned connection

hydraulic ram

timber deck screwed to frame

Apparently, the studio’s goal was achieved and this bridge became a new London’s attraction.

The idea is so smart and simple, that I can just admire and sigh: «Why didn’t I even think about that?»

Eh. 35

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SURFACES

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SURFACES

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EXERCISE 3

Canopy Design Proposal 18. 11. 2013 Design of a canopy over entrance to an airport terminal

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SURFACES

(1) hyperbolic units

sharp angle created by junction of two hypar units is an obstacle for taking precipitation aside

that is why I rejected an idea of hyperbolic geometry and decided to design another structure

(2) negative curvature units

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the same structure made of timber

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SURFACES

AN EXAMPLE OF HYPERBOLIC STRUCTURE TACHKEMONI CANOPIES The structure is based on the interaction between the form (hypar – hyperbolic paraboloid) and the membrane forces, which creates a hightension field

form

forces

The client’s brief stated that the canopies, envisaged as traditional transparent roofs, had to cover part of the playground. The design of a glazed or transparent roof is far too often conceived as the addition of a series of elements, fulfilling only one function. In this analytical design approach the glass shelters people from the rain and lets the light in, the glass slats connect all the elements together, the beams carry the weight and transfer the loads to the columns and further to the foundations. The Tachkemoni canopies were not conceived to be yet another accumulation of horizontal and vertical elements but to be a quest for an object that expresses structural unity.

One element – the canopy – should fulfill all the functions at the same time. This holistic approach led to the simultaneous design of a shelter and a structural surface element. In 1999, at the time of the Tachkemoni design, the most appropriate material to span and shelter the 263 m2 playground area was a curved pretensioned polyvinyl chloride membrane. The membrane shape was found intuitively by using a hyperbolic paraboloid membrane tensioned against a looped tubular frame.

In plan, the surface area of the small canopy is a circle of 12m diameter, the large one an ellipse of 16m by 21m. Nonlinear structural analyses of the entire system took into account the deformation before and after the membrane was pretensioned, as well as the construction method. The construction sequence turned out to be an engineering challenge; while tensioning the membrane against the frame, both the ring and the columns experienced significant displacement. The tops of the columns were displaced by 10cm. In practice this meant that they had to be initially fixed skew to the foundations. When the membrane had been completely tensioned, the columns, in their permanent state, turned out to be perfectly vertical.

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MULTI-PURPOSE HALL IN LEUK Generation of hyperbolic paraboloid

as ruled surface

as translational sur- as a group of identical face parabolas suspended between two vertical parabolas

The hexagonal multi-purpose hall is covered by a timber shell of six identical hyperbolic paraboloid segments.

The 260 m2 roof is supported at the six low points.

Each segment was produced on a jig using two diagonal layers of 24mm boards and edge members of glued laminated timber.

The parallel boards were curved and laid without open joints.

as a group of identical vertical parabolas suspended from a parabola

with all horizontal sections as hyperbolas

The boards were glued together and to the edge members using resorcinol resin, with pressure applied by nails and screws.

The finished segments were lifted into place by crane and joined together. The underside has been left exposed, while the topside is insulated and covered with a synthetic roofing felt.

Corner details for hyperbolic paraboloid shells two diagonal layers of boards with two-part edge member, glued corner reinforcement

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plywood or steel corner rein- edge member notched to ac- plates let into slits, plus dowforcement nailed comodate plate, plus glued elled hardwood fillet timber filllet

SURFACES

LEISURE POOL IN FREIBURG Hyperbolic paraboloid shell

cantilever shells supported at three points, plus ties

cantilever shells with cantilever shells sup- strips of roof glazported at four points, ing, supported at five points, plus ties plus ties

A sequence of 10 hyperbolic paraboloid shells forms the roof over the swimming pool. Each shell segment rests on four reinforced concrete columns placed in two rows 21 m apart.

The segments cantilever out at the facade and the high points t mid-span are supported by struts.

The three layers of 22 mm diagonal boarding on the shell segment enable each one to act as a shear-resistant secondary load-bearing system.

The edge members are two-part, twisted, glued laminated sections. The joints between the segments are used to admit daylight and for ventilation.

Overall stability is guaranteed by the shell segments acting as plates. Continuity results from the trussing and the fixed-base columns.

The shell segments were built on the ground adjacent to the site and lifted into place with a crane.

Make-up of hyperbolic paraboloid shells round-section members and ribs, with diagonal layers of boards

two diagonal layers of boards three diagonal with nail-pressure glued two- boards part edge member

layers

of twisted glued laminated timber edge members and ribs

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REVIEW OF TYPES OF STRUCTURES AND DETAILING

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SURFACES

Designing a fanlike structure

Shrub Tables by Zhili Liu

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Hyperbolic parabaloid structures

Bar Table

by M책ns Salomonsen 48

Arc Table

by Foster+Partners

SURFACES

Cable-stayed structure Flap stay with pull cable

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SUPERSAM MARKET IN WARSAW

Complex type of folded-plate stiffening in which tensioned and compressed elements are balanced against one another

the outside backstays was eliminated by adding compressive struts that are almost horizontal to equilibrate the pull of the cables

folded pattern

plate

triangular steel frames

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the struts were curved to become arches that support half the roof load directly

The alternation of cables and arches produces the folded plate pattern. Each arch consists of a pair of steel channels.

Another pair of steel channels provides a path for each cable. Short lengths of steel angle connect the arches and cables to frame the surfaces of the folded plate.

The steel framework was prefabricated in large sections that were erected on temporary supports with the aid of a crane. Then the cables were threaded through the framework and tensioned with hydraulic jacks.

The roof was covered with sheet metal on the outside and wood on the inside.

Triangular steel frames on the roof of the central structure prevent lateral movement of the cable under asymmetrical loadings.

SURFACES

each arch consists of a pair of steel channels

clerestory lighting

wood slats on the underside of the roof

sheet metal outside covering

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FOLDED PLATE PATTERN

Folded plate variations

in solid-web or box construction

as framework

as truss

as frame

as folded plate to be designed for: f≥1/8

Folded plate hut in Osaka by Ryuichi Ashizawa

Aluminium Chair

by Tobias Labarque

as arch

for solid-web beams, glued laminated timber or plywood with transverse ribs as compound section for transverse bending: d≥h/20 - h/30 for truss: d≥1/4 - 1/6

Orikomi lamp by blaanc

Possible deformations under a symmetric loading due to snow and wind. Design simplified according to beam theory, sloping surfaces as T-beams, with rigid corners as continuous system

buckling of one plate

buckling of both plate

displacement of bottom edge buckling of both plate

Bracing against critical deformation of outer edge as a result of an unifirmly distributed load on one side

edge stiffening in plane of plate

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edge beam perpendicular to plane of plate

edge beam as a horizontal prop

SURFACES

ADVANCED ENGINEERING BUILDING A major part of the Advanced Engineering Building is the 500 seat auditorium and with vast open plan requirements a timber trussed roof system was chosen to span the 25m (30m overall). The trusses are constructed using laminated timber beams with each chord consisting of 2no. 280×83mm bolted together while at the nodes a 10mm plate is ‘flitched’ for added for strength. Tilted at 50deg from vertical each pair of trusses create a dramatic series of ‘V’ shaped profile to the ceiling which is in keeping with the inherent triangular forms of the truss.

HARTWALD CLINIC PAVILION A multi-purpose hall on a hexagonal plan measuring 32m across and covered by a radial folded plate construction. Roof plates resolves into triangular trusses, with 140x240mm and 180x240mm glulam sections. A glulam tension ring resists the horizontal thrust due to the vertical loads. Forces from horizontal loads are transferred into concrete walls. Steel columns arranged in pairs in the centre of the facade carrying the roof. Connections use plates let into sits and steel brackets, fixed with concealed nailing or dowels. There is a glulam node at the apex. Bracing at roof level is by way of the trusses

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THE MATERIAL

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SPECIES OF WOOD Conifer wood (softwood)

Fir

Spruce

Pine

Larch

Cedar

european silver fir

norway spruce

austrian pine

european larch

aromatic red cedar

470 kg/m³

500 kg/m³

660 kg/m³

600 kg/m³

not so easy to treat because of presence of firm swirls

easy to treat, moderate disposition to buckling; high resin content can make treatment difficult

very dense, hard, durable timber with a high resin content

lightweight and soft timber

decays easily, but then the threat of buckling is low

prone to decay because of high natural moisture content

decay-resistant

high decay resistance

low insect resistance

not exposed to insects attack

high insect resistance

Poor conductor of heat, so it can be used as good insulator for heat, noise and for electricity.

It is a cheaper alternative to oak for external uses, and can be used for glulaminating and other timber engineering methods.

lightweight and soft timber

Average density 450 kg/m³ Treatment no resin ducts, easy to treat Moisture prone to decay Insects no insect resistance

low insect resistance

Application Fir is light and soft, but nevertheless has good flexibility and elasticity properties for its relatively light weight.

Internal uses, external with preservatives, frames, core and veneer for plywood, poles, crates, industrial uses.

Spruce is light and soft, As pitch pine (heartbut nevertheless has wood) for highky good strength and elasstressed internal and ticity properties for its (with preservatives) for relatively light weight. external uses, internal Internal uses, external floor civerings, plywood, with preservatives, as red pine (sapwood) frames, core and veneer for internal uses. Winfor plywood, poles, dows, facade panelling, crates, industrial uses. furniture

rough sawn fir lumber of spruce planks of Kamppi Alpine Cabin by Scott & Scott Chapel by K2S Architects

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pine roof of Design Hotel

by Pieta-Linda Auttila

larch cladding of Ty Pren House by Feilden Fowles

Low stress external and internal uses with good dimensional stability, linings, shakes and shingles

artist cut cedar shingle siding, by Bruce Frasier

THE MATERIAL

Deciduous wood (hardwood)

Beech

Maple

Oak

Ash

Birch

european beech

norway maple

black oak

european ash

european birch

730 kg/m³

590 kg/m³

690 kg/m³

710 kg/m³

630 kg/m³

crackes, cleaves and buckles, but thanks to homogeneous structure it can be treated easily

easy to treat, not prone to buckling

flexible, easy to treat

light and easy to treat, but hard to cleave; can buckle and crack during treatment.

prone to decay

low insect resistance

In steamed condition it is very flexible that allows to make curved elements and shells Due to its firmness it is used as massive construction elements, as footsteps, floors and furniture frames

Beech Bend Park Wooden Coaster, Kentucky

easy to treat, and easy to split

sensitive to humidity changes

decay resistance very low insect resistance, especially to common furniture beetle

high enviromental resistance

without special protection is exposed to decay and insects attack

prone to insects attack if

humidity grows flammable

Is used for fittings and wood turning, for veneer and parquet flooring

maple flooring in Navarra General Archive

In steamed condition it is Highly stressed, very flexible (more than external and internal beech), that allows to uses, parquet flooring, make curved elements and high-quality veneers; shells storage barrels, hydraulic and bridge engineering

white oak elliptical shell, Shoffice by Platform 5 Architects

steam bent ash table

by David Colwell

It can be turned, profiled and carved and is well-suited to «peeling» and cutting.

Veneer, plywood, furniture

birch plywood

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CROSS LAMINATED TIMBER Cross-laminated timber (CLT or ‘Crosslam’ or ‘Xlam’) is produced from layers of spruce wood that are arranged crosswise on top of each other and glued to each other with a pressing power of 0.6 N/mm² to form large-sized solid wood elements.

The crosswise arrangement of the longitudinal and transverse layers reduces the swelling and shrinkage of the wood in the plane of the panel to an insignificant minimum and considerably increases the static load-carrying capacity and dimensional stability.

ASSEMBLY The cut-to-size CLT solid wood elements are delivered to the construction site just before they are needed, and there they are assembled by expert timber construction companies or construction firms using a building crane in the shortest possible construction period. The links created between tradition, well-founded craftsmanship and state-of-theart timber construction technology enable individual construction with lasting value and a particular focus on the environment and energy consumption.

ADVANTAGES

tion elements

• Ecologically sustainable building material • Recommended in terms of building biology • Positive ecobalance • Healthy, comfortable room climate • Solid wood construction with lasting value • Freedom in architectural implementation • Flexible design without a grid pattern • Compatible with steel, glass and other materials • Excellent static properties • Increasing space thanks to slender construc-

2.95 m

0.50 m 16.50 m

Maximum size of CLT panel

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• Technically approved and CE certified building product • Quality controlled production • Prefabricated elements with high dimensional accuracy • CNC controlled cutting of the elements • Delivery directly to the construction site • Easy to install • Short construction period • Dry construction method

Another encouraging conclusion is that CLT is evidently well suited to infill construction.

This is because, when compared to other materials, the CLT site is less disruptive to neighbours on account of the rapid construction and quieter building activities using lightweight power tools. These tools pose a lower hazard to operatives’ health than the heavier equipment needed to drill into concrete, masonry and steel structures.

THE MATERIAL

GLUED LAMINATED TIMBER Glued laminated timber (Glulam) is a type of structural timber product comprising a number of layers of dimensioned timber bonded together with durable, moisture-resistant structural adhesives.

By laminating a number of smaller pieces of timber, a single large, strong, structural member is manufactured from smaller pieces. These structural members are used as vertical columns or horizontal beams, as well as curved, arched shapes. Glulam is readily produced in curved shapes and it is available in a range of species and appearance characteristics to meet varied end-use requirements. Connections are usually made with bolts or plain steel dowels and steel plates.

Glulam has much lower embodied energy than reinforced concrete and steel, although of course it does entail more embodied energy than solid timber. However, the laminating process allows timber to be used for much longer spans, heavier loads, and complex shapes. Glulam is two-thirds the weight of steel and one sixth the weight of concrete – the embodied energy to produce it is six times less than the same suitable strength of steel. Glulam can be manufactured to a variety of straight and curved configurations so it offers architects artistic freedom without sacrificing structural requirements. Wood has a greater tensile strength relative to steel – two times on a strength-toweight basis – and has a greater compressive resistance strength than concrete. The high strength and stiffness of laminated timbers enable glulam beams and arches to span large distances without intermediate columns, allowing more design flexibility than with traditional timber construction.

The size is limited only by transportation and handling constraints.

LAMINATED VENEER LUMBER Laminated veneer lumber (LVL) is an engineered wood product that uses multiple layers of thin wood assembled with adhesives. It is typically used for headers, beams, rimboard, and edge-forming material. LVL offers several advantages over typical milled lumber: Made in a factory under controlled specifications, it is stronger, straighter, and more uniform. Due to its composite nature, it is much less likely than conventional lumber to warp, twist, bow, or shrink.

LVL is similar in appearance to plywood without crossbands, and is typically rated by the manufacturer for elastic modulus and allowable bending stress.

A comparable material is parallel strand lumber (PSL), which is used in the same applications. Rather than being manufactured from full, parallel veneers, Parallel strand uses veneers with more defects in a more random-looking pattern. Laminated strand lumber (LSL) is another similar type that uses smaller veneers, and so is similar to oriented strand board (OSB) in appearance. Laminated veneer, parallel strand, and laminated strand all belong to the general category of structural composite lumber.

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PLYWOOD Plywood is a manufactured wood panel made from thin sheets of wood veneer. Plywood layers (called veneers or plies) are glued together, with adjacent plies having their wood grain rotated relative to adjacent layers up to 90 degrees.

All plywoods bind resin and wood fiber sheets (cellulose cells are long, strong and thin) to form a composite material. This alternation of the grain is called cross-graining and has several important benefits: it reduces the tendency of wood to split when nailed at the edges; it reduces expansion and shrinkage, providing improved dimensional stability; and it makes the strength of the panel consistent across all directions. There is usually an odd number of plies, so that the sheet is balanced — this reduces warping. Because plywood is bonded with grains running against one another and with an odd number of composite parts, it is very hard to bend it perpendicular to the grain direction of the surface ply.

A typical plywood panel has face veneers of a higher grade than the core veneers. The principal function of the core layers is to increase the separation between the outer layers where the bending stresses are highest, thus increasing the panel’s resistance to bending. As a result, thicker panels can span greater distances under the same loads. In bending, the maximum stress occurs in the outermost layers, one in tension, the other in compression. Bending stress decreases from the maximum at the face layers to nearly zero at the central layer. Shear stress, by contrast, is higher in the center of the panel, and zero at the outer fibers.

ORIENTED STRAND BOARD Oriented strand board (OSB) is an engineered wood particle board formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations. OSB may have a rough and variegated surface with the individual strips of around 2.5 Ă— 15 cm, lying unevenly across each other and comes in a variety of types.

OSB is a material with high mechanical properties that make it particularly suitable for load-bearing applications in construction. The most common uses are as sheathing in walls, flooring, and roof decking. For exterior wall applications, panels are available with a radiant-barrier layer pre-laminated to one side; this eases installation and increases energy performance of the building envelope. OSB also sees some use in furniture production. OSB is suitable for: timber frame housing; flat and pitched roofs; wall sheathing; flooring; portable buildings; caravans; and agricultural buildings.

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THE MATERIAL

PARALLAM Parallam is the brand name for a structural composite lumber (SCL) product invented, developed, commercialized and patented by MacMillan Bloedel (now Weyerhaeuser). The generic name for the product is parallel strand lumber (PSL).

Parallam is made from clipped veneer strands laid in parallel alignment and bonded with adhesive. It is used for beams, headers, columns, and posts, among others uses.

Parallam is the world’s only commercially manufactured and marketed parallel strand lumber product.

The design values for Parallam, in bending, tension parallel to grain and compression parallel to grain are greater than sawn lumber made from the same or similar species. This is because knots and other imperfections are randomly dispersed throughout the product so that strength variability from one piece to another is less than in solid-sawn wooden beams. Since materials are commonly graded to the lowest 5th percentile of the material’s strength curve, this gives Parallam much higher usable strength. Parallam can be made from any wood species, but Douglas-fir, southern pine, western hemlock, and yellow-poplar are commonly chosen because of their superior strength.

MEDIUM-DENSITY FIBREBOARD Medium-density fibreboard (MDF) is a wood product made by breaking down hardwood or softwood residuals into wood fibres, often in a defibrator, combining it with wax and a resin binder, and forming panels by applying high temperature and pressure. MDF is generally denser than plywood. It is made up of separated fibres, but can be used as a building material similar in application to plywood. It is stronger and much more dense than particle board.

BENEFITS OF MDF • Is an excellent substrate for veneers.

• Some varieties are less expensive than many natural woods • Isotropic (its properties are the same in all directions as a result of no grain), so no tendency to split • Consistent in strength and size • Flexible. Can be used for curved walls or surfaces.

• Shapes well.

• Stable dimensions (won’t expand or contract like wood) • Easy to finish (i.e. paint)

DRAWBACKS OF MDF • Denser than plywood or chipboard (the resins are heavy) • Low grade MDF may swell and break when saturated with water.

• May warp or expand if not sealed.

• Contains urea-formaldehyde which is a probable carcinogen and may cause allergy, eye and lung irritation when cutting and sanding • Dulls blades more quickly than many woods • Though it does not have a grain in the plane of the board, it does have one into the board.

Screwing into the edge of a board will generally cause it to split in a fashion similar to delaminating.

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62

TIMBER TOWERS

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STADTHAUS, LONDON Waugh Thistleton Architects

9 storeys • pre-fabricated cross-laminated timber panels • the 2nd tallest timber residential building in the world • timber species — spruce •

Constructed from cross-laminated timber panels (CLT) from the first floor upwards, Stadthaus is considered to be the 2nd tallest modern timber structure in the world. The nine-storey building is the first of this height to construct load bearing walls and floor slabs as well as stair and lift cores entirely from timber.

SUSTAINABILITY According to the Australian Timber Development Association, the consultant team, “calculated that the 9 storey residential building could store 181 tonnes of carbon when completed and by not using traditional concrete methods could save a further 125 tonnes from entering the atmosphere during the construction process.”

CLT lowers the energy used in construction, reduces heat loss during occupation by improving insulation and airtightness, and it is also very easy to demolish and recycle at end of life. Mechanical ventilation of all rooms includes a heat recovery system that retains 70% of the heat that would normally be lost when return air is expelled. Photovoltaic (PV) panels on the roof generate a modest supply of renewable energy.

The Stadthaus provides a high acoustic performance. CLT panels have a significantly higher density than timber frame buildings. They provide a solid structural core on which different, independent and separating layers can be added. The layer principle overcomes any sound transfer issues. With a consistent and economic layering strategy of walls with joints in front of the party walls, floating floor build-ups and suspended ceilings, the designers achieved sound reduction and thermal performance that exceed UK requirements.

The façade employs wood: the 5000 panels (each 1200mm x 230mm ) are made up of 70% waste timber. The architects designed the façade by firstly recording the changing light and shadows formed on the vacant site by the surrounding buildings and trees.

Then they modelled the pattern through a sun-path animation and, finally, wrapped the pixilated and blurred image around the building. The balconies and windows punctuate the rhythm of the abstract image.

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TIMBER TOWERS

STRUCTURE The tower is a cellular structure with apartments in a honeycomb pattern around a central core. The load-bearing elements (lift shafts, stairwells, all external and some internal walls) provide exceptional resistance to progressive collapse and good acoustic separation between apartments and lift shaft.

in areas of high stress where walls press into the floor, self-drill woodscrews or nails are driven into the floor to distribute the surface load deeper into the panel

insulation is installed on the exterior of the wood panels elevator shafts and stairwells have double walls with an insulating layer

A

B

metal brackets and screws are used to join panels to-

concrete sub-structure transfers the loads to the foundation and provides a level threshold for the timber, at either ground or first floor level

Screws and angle plates secured the joints. Stresses are generally very low throughout the structure although, at points where cross-grain pressures are high, screws were added to reinforce the timber locally. Progressive collapse is avoided by providing sufficient redundancy so that any single elements can be removed.

The untreated timber relies on the building envelope for protection from damp and rot. While installation in wet weather was inconvenient, it had no effect on the panels because the system releases moisture readily as it dries.

COMPETING WITH CONCRETE Although more expensive than an equivalent reinforced concrete frame, CLT brought significant overall savings by making a radical cut in the building programme. For example, an equivalent concrete building was estimated to take 72 weeks, whereas the CLT solution required only 49 weeks.

The erectors brought a large mobile crane, which eliminated the need for a tower crane that would normally be needed for a concrete structure. Scaffolding was needed to fix the cladding, but not to erect the wood structure.

The CLT structure represented three days’ production at KLH’s factory. And the rapid installation played an important role here. The four-man Austrian crew was on site three days a week and accomplished the entire superstructure erection in 27 working days, over nine weeks.

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The +/- 5mm tolerance was achieved with the timber construction: 10mm are normally expected in concrete structures. The consequence of tight tolerances is the ease of fitting the structure together, its good airtightness and the ease of fixing cladding.

Floor-to floor movement due to moisture and creep is estimated to be 3mm, which gaps in finishes can tolerate. Also, by avoiding concrete cores, there is not the differential movement to resolve between concrete and timber that occurs with conventional timber frame.

Installation of building services has proven easier than expected, so future projects might expect better prices as this experience is taken into account. Cables and pipes were generally surface mounted with simple screwfixed straps, the plasterboard was installed on metal tophat sections. In contrast, Austrian practice takes advantage of the factory’s ability to cut chases for service runs. Hence, they would normally fix the plasterboard directly to the CLT panels.

Another encouraging conclusion is that CLT is evidently well suited to infill construction. This is because, when compared to other materials, the CLT site is less disruptive to neighbours on account of the rapid construction and quieter building activities using lightweight power tools. These tools pose a lower hazard to operatives’ health than the heavier equipment needed to drill into concrete, masonry and steel structures.

DETAIL A: SECTION AT EXTERNAL WALL

DETAIL B: SECTION AT ELEVATOR SHAFT

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TIMBER TOWERS

3rd floor plan (apartments for tenants of Metropolitan Housing Trust, 1-3 levels)

5th floor plan (private apartments, 4-8 levels)

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FORTÉ, MELBOURN 10 storeys • 32,17m in hight • the tallest timber residential building in the world • timber species — spruce •

759 CLT panels comprising 485 tonnes of timber were fabricated by KLH and shipped to Melbourne via the Suez Canal. Some panels measure 16.5x3m, with walls and floors 128mm and 145mm thick respectively.

SUSTAINABILITY According to the company, its construction was 30% more efficient and faster thanks to the ease of transportation and installation of construction elements, generating less traffic of machinery and fewer CO2 emissions and waste. The project succeeded in reducing 1,400 tons of CO2 emissions during construction compared to the use of concrete and steel - the equivalent of taking 345 cars off the road. This construction method provides a better thermal performance and reduces energy costs and water generating savings for residents averaged nearly $ 300 per year. The analyzes also show a 22% reduction in greenhouse gas emissions in a cycle of 50 years.

This bulding offers better therperformance and requires less energy to heat and cool - which means reduced energy and water costs which averages savings of a $300 per year or up to 25% less than a typical code-compliant apartment.

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mal

TIMBER TOWERS

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BRIDPORT HOUSE, LONDON Karakusevic Carson Architects

8 storeys • pre-fabricated cross-laminated timber panels • the largest timber residential building in the world • timber species — spruce •

A multi-storey building has been constructed entirely from CLT including the ground floor. One of the reasons it has been designed in this way is due to the presence of a large Victorian storm relief sewer running beneath the site making it unsuitable for a heavy traditional concrete frame structure.

The unique properties of CLT’s engineered strength combined with its light weight made it the ideal solution to overcome this problem. Construction of the CLT frame took 10 weeks of clean and quiet installation, considerably faster than a conventional reinforced concrete frame, which it is estimated would have taken around 21 weeks.

SUSTAINABILITY According the calculations of the Centre for Sustainable Development at the University of Cambridge, total difference of CO2 released into the atmosphere between a conventionsl concrete frame and CLT construction was 892 tonnes of CO2 which is equivalent to 12 years of operational energy required to heat and light all the dwellings at Bridport House; alternatively it would take 61 years to save the same amount of carbon as the planning requirement of 20 per cent renewables.

When the sequestered carbon locked up in this 1,576m3 timber structure is added to the carbon avoided, the total figure is 2,113 tonnes of carbon and this is equivalent to 29 years of operational energy or, with 20 per cent renewable energy, it would take 144 years to save the same amount of carbon.

CLT structure is significantly lighter than its concrete frame equivalent and it is prefabricated off-site which makes the onsite construction schedule shorter and consequently cheaper. The only drawback is that most CLT is currently produced in Austria and transported by road.

STRUCTURE A plinth of dark brownish brick defines the band of maisonettes, rising to the north to clad the five-storey block. Two-fifths of the way along its length, the building climbs up to eight storeys, clad in a lighter white brick.

Stacks of balconies project 2.5m from the facade along both east and west elevations, braced with angled tensile rods, giving the building the air of a pricey docklands warehouse conversion.

Care has been taken to express the verticality of 70

TIMBER TOWERS

ground floor

2nd floor

7th floor

the block, so it reads as more of a tower-like form than its dimensions betray, avoiding the squat bearing of many similar schemes.

At its south-western corner the form is mitred back to create a fifth elevation, punctuated by a stagger of copper-clad bay windows, positioned to pick up the afternoon sun and frame views from quirky day-bed cubby holes in the flats.

The southern elevation, also angled to form a prow-like point towards the park, confounds any suspicion that this could be social housing, being fully glazed with floor-to-ceiling windows that open out on to huge recessed balconies with panoramic views across London.

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Site Constraints Plan

Loadbearing structure 72

TIMBER TOWERS

Carbon emisson calculation for Bridport house

piling

existing storm water relief sewer

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PROBABLE FUTURE OF TIMBER MULTI-STOREY BUILDINIGS

up to 30 storeys • integral strenght of laminated strand lumber (LSL), cross-laminated timber panels (CLT) and Laminated veneer lumber (LVL) panel products with introduction of steel •

Option 1, a building height up to 12 storeys is achievable employing structural core walls and glulam columns at the perimeter as the supporting structure. It offers the greatest amount of flexibility in the design of its interior partitioning.

This structural configuration bears closest resemblance to the typical concrete benchmark in that it utilizes a structural core and perimeter columns that affords it a free-plan.

In option 2 and 3, which achieve greater building heights up to 20 storeys, additional structure is required. Structural interior walls and structural exterior walls provide this additional support in options 2 and 3 respectively.

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TIMBER TOWERS

FFTT SOLUTION1 FFTT is a unique tilt-up system that effectively balloon-frames Mass Timber panels in a cost effective and simple manner to build Tall Wood buildings. The system uses a strong column – weak beam structural approach that is described in detail later in the report. FFTT was first developed by Michael Green and Eric Karsh in 2008. Mass Timber panels are used for floors, walls and the building core with engineered wood columns (up to 12 storeys) and steel beams and ledger beams (12 storeys and up) integrated into the Mass Timber panels supporting floors. The introduction of steel allows for the ‘weak beam’ solution and great flexibility for the system to achieve heights with a predominantly all-wood solution. FFTT uses the integral strength of CLT, LSL or LVL panel products. The FFTT system is adaptable to many building types, scales and locations and allows for the fast erection of very simple and structurally sound buildings.

The structural configurations, in addition to determining the achievable building heights will impact both the design of the envelope and floor plan of the building

1 More details: Michael C Green, The Case for Tall Wood Buildings, 2012

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In options 3 and 4, where additional structure is required for the increase in building height, constraints are placed on the design of either the interior partitions or envelope. As a result, these configurations can be more advantageously applied to specific uses. For instance, where interior walls are utilized as structure, a residential application would be appropriate where these structural walls could double as unit demising walls.

For option 4, as in option 2 and 3, structural interior walls and structural exterior walls provide additional support.

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TIMBER TOWERS

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CONSTRUCTION SEQUENCE

STEP 1

STEP 2

STEP 3

STEP 4

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TIMBER TOWERS

STEP 5

STEP 6

STEP 7

STEP 8

79

STEP 9

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TIMBER TOWERS

GREEN M. CASE STUDY FACADE SECTION

GREEN M. CASE STUDY CURTAIN WALL FACADE SECTION

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PROBABLE FUTURE OF TIMBER MULTI-STOREY BUILDINIGS C.F. Møller Architects

34 storeys • wooden structure with stabilizing concrete cores • Each apartment will have an energy-saving, glass-covered veranda, while the building itself will be powered by solar panels on the roof.

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TIMBER TOWERS

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ENVIRONMENT

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ENVIRONMENTAL IMPACTS OF TIMBER STRUCTURES The use of more timber and wood products in design, construction and operation can economically reduce the carbon footprint and environmental impacts of buildings. Timber can displace more fossil-fuel intensive construction materials such as concrete, steel, aluminium, and plastics, which can result in significant emission reductions.

Wood is renewable material Wood is stored solar energy Photosynthesis converts solar energy into wood. About 50% of its mass is carbon, which is fixed through absorption of the greenhouse gas carbon dioxide.

Wood is a global carbon store Forests and wood products make an effective contribution to protecting the climate. The use of wood reduces the consumption of non-renewable fuels and products made from non-renewable resources Wood as building material ensures a healthy interior climate Timber products at the ens of their life cycle can be used in different ways: biological decomposition, material recycling or energy generation

Buildings consume great quantities of materials, energy and other resources and generate significant greenhouse gas emissions and other environmental impacts during their lifecycle. The use of renewable materials and energy sources in sustainable building design can reduce these emissions and impacts significantly. This will deliver benefits as: 1. Timber has lower carbon and environmental impacts than comparable building materials.

2. Timber production is a low energy and low impact process.

3. Timber provides solutions that meet regulatory requirements on fire safety.

4. Timber buildings have high performance.

5. Timber construction is locally supported.

Potential exists to increase timber’s use in: • Timber floors and floor systems in houses and other buildings, • Timber framed structures in school halls and assembly buildings, • Fire and sound resistant timber walls, lining and cladding.

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ENVIRONMENT

THE CARBON CYCLE OF TIMBER AND WOOD-BASED PRODUCTS Timber production makes a positive contribution to reducing carbon emissions by being part of the short term carbon cycle that involves trees absorbing carbon dioxide from the air, releasing oxygen and storing the carbon in the wood.

Using trees for timber and other wood products in this way creates space in plantations and hardwood production forests for replacement trees to absorb more carbon from the atmosphere. What little energy is needed to process and dry wood to make timber is commonly produced from sawmill residues such as bark and sawdust generated by converting a tree into sawn timber.

Excess sawmill residue is used in the manufacturer of long-life panel products such as particleboard or medium density fibreboard (MDF).

The carbon in the timber, which has been absorbed from the atmosphere, is stored for long periods of time in an array of timber products such as house frame, roof trusses and flooring.

When a home is demolished or renovated, waste timber that cannot be reused can be recycled into a range of products including particleboard. Timber not suitable for reuse or recycling can be utilised to generate renewable energy, releasing the carbon back into the atmosphere to be reabsorbed by the growing trees. For waste not suitable for reuse, recycling or renewable bioenergy, Australian research is showing that end-of-life timber stores the carbon for very long periods of time in well-managed landfills.

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CARBON FOOTPRINTING According to University of Canterbury research1, the 60-year life cycle of the building is dominated by emissions due to the operation of the building during occupancy despite of what material was used for construction. In this study there are presented results of a life-cycle assessment (LCA) for Global Warming Potential (GWP) and energy use of four similar open-plan building designs – Concrete, Steel, Timber and TimberPlus – all based on an actual six-storey 4,200 m2 building. The Timber concept was designed with post-tensioned timber structure using laminated veneer lumber (LVL); in Timber Plus concept the use of timber was increased owing to wooden exterior cladding, windows and celings.

This diagram shows that the GWP of the materials themselves does not directly influence the GWP of the building during the operational phase, but during the initial embodied phase timber buildings produce less CO2 emissions.

The greatest reduction in each building’s carbon footprint can be brought about by reducing the emissions associated with the activities of this operational phase, such as through better overall building design, passive heating and cooling, the use of phasechange materials, energy efficient lighting, etc.

Actually it is hard to rely entirely on such researches, because most part of them is presented by companies that produce wooden products. Nevertheless it is seems to be intuitively clear that timber has better enviromental impact, than steel or concrete, but I still doubt if it is not a manipulating with facts.

1. Johns S., Nebel B., Perez N., Buchanan A. Environmental Impacts of Multi-Storey Buildings Using Different Construction Materials, Research report 2008-02, University of Canterbury Christchurch, 2009

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ENVIRONMENT

According to the New Zealand timber Design Guide 2007, the following table presents the quntity of carbon emission per year of single-family house: Timber Plus

Timber

Steel

House size

200 m2

200 m2

200 m2

Floor

Timber

Concrete

Concrete

Frame

Timber

Timber

Steel

Windows

Wooden

Aluminium

Aluminium

Cladding

Timber

Brick veneer

Brick veneer

Roofing

Long run iron

Long run iron

Long run iron

Timber

Concrete

Concrete

[-20,68] tonnes

18,73 tonnes

32,77 tonnes

Decking (30 m2) Carbon emission per year

According to research by the australian Cooperative Research Centre (CRC) for Greenhouse Accounting, the following data represents gas emissions from the manufacture of different building components in a single-family house:

Therefore timber in building reduces carbon emissions in three ways: the carbon stored in growing trees is retained and stored in the timber for at least the life of the building; using wood instead of energy intensive materials avoids the emissions associated with producing those materials; increased timber use supports the economic expansion of forests through the landscape: forests are significant carbon sinks.

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REFERENCES 1.

2.

3.

4.

Detail, Timber Construction Manual, Birkhäuser, 2004 Footbridge Awards Review, 2011 Green M., The Case for Tall Wood Buildings, 2012 Johns S., Nebel B., Perez N., Buchanan A. Environmental Impacts of Multi-Storey Buildings Using Different Construction Materials, Research report 2008-02, University of Canterbury Christchurch, 2009 5. KLH Massivholz GmbH, Component catalogue for Multi-storey Residential buildings, 2012 6. KLH Massivholz GmbH, Cross-Laminated timber, 2013 7. New Zealand timber Design Guide, 2007 8. Ney L. Shaping Forces, Bruges: A+Editions, 2010 9. Ochsendorf J.A., Sustainable Engineering: The Future of Structural Design, Massachusetts Institute of Technology, 2005 10. Ritter M., Timber Bridges: Design, Construction, Inspection, and Maintenance, Washington, DC, 1990 11. Robinson M., Kile G., Forests, Wood and Australia’s Carbon Balance 12. Tas L.M., Master Thesis ‘Curved Folded Timber Plate Structures’, Eindhoven: Eindhoven University of Technology, 2013 13. Trautz M., Herkrath R., The application of folded plate principles on spatial structures with regular, irregular and free-form geometries, Aachen: Aachen University, 2009 14. UNBOUND Uncommissioned Report, Timber Technology, University of Limerick, 2012 15. Yilmaz F., Static and Dynamic Analysis of Alvsbaska Timber Bridge, Karlskrona: Bleckinge Institute of Technology, 2012 16.

17.

18.

19.

20.

21.

22.

www.wood-database.com www.americanhardwood.org www.nzwood.co.nz www.nztif.co.nz www.timber.net.au www.timberinconstruction.co.uk www.dataholz.com

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Tomorrow is wooden