Structural Design Guidelines for Young Architects, by ROBERTO MARÍN,

Structural Design Guidelines for Young Architects STRUCTURAL DESIGN GUIDELINES INTRODUCTION The aim of this document/form is to allow you to intimate with your building or structure. This intimacy means to achieve a deeply knowledge of the characteristics and main design principles of your project. The final goal of this study is to “name” what you are proposing. You might think that a name is not a great fortune, but to own a name is the door for further evaluations and discussion. The name I want you to put to your building/structure/project could be like this: 65WC+35GC+PC+F, that means that the structure design is conducted in a 65% by Wind load, in a 35% by gravity (weight), the material/technology that is going to support the structural solution is Prestressed Concrete, and finally, the structural strategy/layout that is going to adapt the structural technology to the application that your are working on, is a Frame disposition (beams and columns).

Below, some previous design stages are summarized; some of them are marked as Study that means that you are invited to investigate about it, in order to achieve personal criteria to do a structural selection/decision in further choosing stages.

STUDY nº1: SITE, ENVIRONMENT Just the beginning of your journey; three investigations are required; Is your design in danger to suffer, because its location, some of the following risks?

‐STUDY 1.1 “CONTINUOUS NATURAL HAZARDS”

CHEMICAL ATTACK. The environment that surrounds your project is going to seriously determine, the structural materials and technology of your selection. The salty ambient that is present in close to sea cities or the chemicals that are easy to find in a pool or in a factory, and situations like these, have terrible consequences on the DURABILITY of your design, allowing dangerous processes as CORROSION. The common practice is to design to last at least 50 years.

GROUND CHEMICAL ATTACK. Ground chemical composition might be tested in order to adopt special measures at the building’s foundations. To determinate the quality of the ground where you are designing is out of the scope of our study, but, some land areas are well characterized in general terms, so maybe, you can get this information. For example in Madrid everybody knows that the ground has a medium bearing capacity and the chemical attack is very unusual. ‐STUDY 1.2 “ACCIDENTAL NATURAL HAZARDS”

EARTHQUAKES. One of the greatest and challenging natural forces. It has a tremendous impact on the structure and building’s shape.

TSUNAMI

SLOPE INSTABILITY. Depending on the cartography of the site

Roberto Marin

Structural Design Guidelines for Young Architects

FIRE. The structural integrity must be guaranteed for a period of time depending on the use of the building to allow people to evacuate the building.

These natural issues could define a load (see next study), to invalidate a structural strategy or material, or just could create a warning of use. A classic warning of use comes from FIRE resistance. Steel is the worst material to resist fire but, if you have chosen laminate steel as structural material, because your geometry (and/or the set of loads that your structure has to resist) makes it appears as the most suitable technology, you must consider that the steel probably will need to be protected with extra nonstructural materials. ‐STUDY 1.3 “LEGISLATION” I invite you to take some control about the current structural codes in the country or region of your interest. I am not asking for a deep study, just to know something like how British Standards or Eurocode defines building loading.

STUDY nº2: LOADS, USE, GEOMETRY and PROGRAM You have to analyze your proposal with the aim to clarify which characteristics are going to dominate its behavior. There are not clear rules to complete this stage, just the common sense. If your structure is very tall and slender, wind action will be very important in the design, if it is your desire to build a “tunnel like” building, earth pressure will determine the structural strategy and construction, if your building is not very tall, not very irregular, not very anything, you will have a structure mainly design to accommodate gravity loads. Of course there are not pure situations, so you will have a combination of various different loads with different levels of importance, defining different structural philosophies that you, as a designer, have to combine in a single final layout. Following these reflections you will finally get a set of “driver of philosophy” loads for your further structural conceptual design, like “35%wind load + 40%seismic action + 25% gravity. The ratios doesn’t come from a mathematical expression, it is just a symbolic number that I leave to your discretion in order to evaluate the relevance of each one.

The main loads that could conduct the design, or activate a “driver of philosophy” are

GRAVITY LOADS:

‐SELF WEIGHT: The weight of the structural elements

‐DEAD LOAD: The “permanent weight” of nonstructural elements like walls, windows, finishing, etc

‐LIVE LOAD: The weight that is caused by the USE of the building. The structure of a theater is very different than a private house structure, just because the different amount of people that can be standing. It is not a permanent load.

‐SNOW

LATERAL LOADS:

‐WIND LOADING

Roberto Marin

Structural Design Guidelines for Young Architects

‐EARTHQUAKE

‐EARTH PRESURE

ACCIDENTAL LOADS:

‐VIBRATIONS

‐BLAST

For further information check your study 1.3 the national and international codes usually define the loads that you have to consider in your design.

CHOOSING nº1: MATERIAL, TECHNOLOGY The materials or technologies frequently used in construction are listed below. I leave to your discretion its election (previous some investigation about how they work, of course), subsequently, we will discuss together the feasibility of your solution and its properties.

CONCRETE. It provides great stiffness, a good stability against fire and a good durability. It has time‐dependent ‐properties, like shrinkage and cracking so, If you load a concrete structure it will suffer a deformation process (deflection) that last to the end of its life.

REINFORCED CONCRETE. It is the regular concrete. The concrete works as a stone resisting compression forces, the steel bars handle the tension forces inside the concrete.

PRESTRESSED CONCRETE the tension forces in concrete are avoided with prestressed steel bars

POSTSTRESSED CONCRETE the same technique but applied after the concrete is made.

STEEL. Laminated steel, it provides a greater flexibility and a greater resistance than concrete.

To materialize special joints is easier than in concrete. It doesn’t have time‐dependent‐ properties as particular as the concrete but, the problem of corrosion is more evident WOOD its behavior depends on ambient parameters as humidity. Its structural bearing capacity is lower than concrete or steel.

NATURAL

LAMINATE. It provides a good behavior in chemical environments. Surprisingly it has a great performance against fire.

CARBON FIBER. An advanced material that is very useful in retrofit projects.

CHOOSING nº2: STRATEGY, LAYOUT Some common structural strategies are listed. I encouraged you to create your own new strategy or your own blend of strategies.

Important note to strategy choosing: when we think about structures we always think about resistance and forces, but your design must fulfill important limitations on deformations

Roberto Marin

Structural Design Guidelines for Young Architects requirements. Deformations can be as dangerous as a lower resistance in terms of security (structural pathologies) but also, it can make the use of the building unfeasible. Laminated Steel is especially sensible to deformations so, usually it is overdesign to avoid great deformations.

The concept of deformations has been taken far beyond the deformation itself, you must include vibrations, movements and other effects that can make the use of the building uncomfortable. Remember the resonance problem of the London Millennium Footbridge.

C2.1 SKELETON. It is a classical contemporary. A combination of “one‐dimensional” structural elements that creates a framework where the building leans. The idea is to distribute structural elements of well‐known behavior. The designer anticipates the behavior of the structure.

C2.1.1 FRAME. The classical among the classic. Just columns and beams

C2.1.2 LONG SPAN FRAMES the structural elements take three‐dimensional layouts to accommodate great spans.

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Structural Design Guidelines for Young Architects C2.1.3 NET. When geometry is complicated the easier way to create the skeleton is to transfer the architectural form to a net of steel bars. limited engineering judgment, just trial and error work by the hand of software applications.

C2.2 SKIN. exo‐structures made of a continuous structural element, as concrete sheets.

C2.3 CABLE. bridges classical approach. Useful for long span roofing.

C2.4 DOME

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Structural Design Guidelines for Young Architects C.2.5 TEXTILE. Tenso‐structures. Textile membranes

CHOOSING nº3: STRUCTURAL ELEMENTS Your strategy needs some structural “units”, some of them are listed.

BEAMS. mainly flexion behavior, horizontal elements COLUMNS. mainly axial behavior, vertical elements WALLS. axial and shear behavior.

TRUSSES. 3D elements composed by a set of other elemental structural members.

SLABS. FOOTINGS. superficial foundation elements PILES. Deep foundation elements SHELLS. All kind of thin 2D structural elements (mainly concrete made) CHOOSING nº4: CONSTRUCTION PROCESS Think about how you are going to build the structure. Many times, the structure, during the construction process, is under a different loading state than in its final disposition.

You have to decide which parts are going to be done in the site and what kind of works you prefer to do in a special workshop.

PRECAST

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Structural Design Guidelines for Young Architects IN SITU RETROFIT PROJECTS. The structural project is more a stages history than a regular project GENERAL STAGES ZOOM IN‐ZOOM OUT, SUMMARY You can complete this journey drawing the structural layout that you have created. It is not necessary to draw something very precise but, four ZOOM levels are required.

First zoom level basic structural diagrams. Just lines to understand how your structural system works

Second zoom level interaction with the rest of architectural elements, a more detailed work to check interactions with the rest of architectural elements. It is understood that you are not going to draw the correct dimensions of the structure, but try to make it reasonable.

Roberto Marin

Strucctural Design Guidelines ffor Young Arrchitects Third zoo om level DETAIL. Just a coouple of tech hnical drawin ngs to explai n how some e nts are goingg to be linkedd one to each h other. Don n’t be afraid iif you don’t structtural elemen exacttly know the number and d disposition of screws, b bolts, welds, etc… just tryy to do it.

Forth zoo om level construction proocess

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