LA 481 Final Project Documenting the Detail: A Bridge Jeremy Johnson Fall 2017
PROJECT STATEMENT One of the most important tasks of a Landscape Architect is connecting people to outdoor spaces. Landscape Architects commonly use bridges to create connections from place to place that would otherwise be limited by topography and waterways, but in the eyes of a Landscape Architect a bridge is more than an access route. Bridges can be places with character. The materials of the bridge mean something. The way the bridge sits on the site says something. The way the materials connect to one another are purposeful. The smallest details tell a lot of information. Inside Pammel Woods, North of Iowa State’s College of Design, is a bridge that crosses Clear Creek. None of the elements of the bridge, neither in materiality or structural construction, go beyond satisfying the function of a typical bridge. It is a timber decking and GLULAM beam bridge with dimensional lumber for handrails. The biggest issue with this bridge is how it
ignores the site conditions. The major site condition this bridge ignores is the creek it crosses. This bridge sits on a wooden foundation which is poorly suited for a site which floods. The water levels during a flooding event are high enough to have stale water in contact with the beams of the bridge. While the GLULAM beams are water resistant due to their sealant production, the life span of the bridge will be shortened after years of water contact during flooding events. My goal in this project is to design and detail a simple timber beam bridge, similar to the existing bridge, but make construction decisions that will elongate the lifespan of the bridge while showing my knowledge of how the materials connect together. The proposed design focuses on raising the bridge on a concrete foundation to alleviate stress from flooding events.
RESEARCH To begin this project, it was first important to understand the materials that I was working with. The materials that I focused on were GLULAM beams, timber decking, and concrete foundations because I already know enough about concrete ramps and dimensional lumber. GLULAM or Glued Laminated Timber beams are made of “wood laminations bonded with (moisture resistant) adhesives, with the grain approximately parallel in lengthwise.” (Thomas Hodne Architects, Inc) “Pound for pound, a GLULAM board is stronger than steel and PG. 1 has, greater strength
has greater strength and stiffness than comparably sized dimensional lumber.” (APA-Engineered Wood Association) “Because of the large size of GLULAM beams, GLULAM beam bridges require fewer beams and are capable of much longer clear spans than conventional sawn lumber beam bridges.” (Types of Timber Bridges, Chapter 2) This research proves GLULAM is a perfect choice for a simple bridge when considering the difference in the amount of materials needed when comparing GLULAM to dimensional lumber. This bridge has to span at least 45’. Similar to beams, GLULAM is highly regarded as a durable decking timber. Dimensional lumber would be considerably cheaper in this scale of the construction. GLULAM decking comes in larger widths closer to 4’ wide (Laminated Concepts, Inc), but the cost of 2”x8”x8’ pressure treated lumber is more reasonable here. There is nothing that I have researched that shows pressure treated lumber having a considerably shorter life span than GLUM decking and because of these reasons I designed with pressure treated Doulas Fir decking. The most important research to this redesign is foundation because this is the only materiality change that I am designing in. It isn’t exactly clear what the construction is for the existing bridge’s wooden foundation, but my guess is it is a wooden pile and core that is below the frost depth. The existing GLULAM beams are fastened on top of the foundation with Hbrackets. The proposed design has an average of 2’ height increase to avoid flood waters. The proposed
poured concrete foundation houses a beam seat or concrete pilaster for the four beams to sit. This will create the strongest connection for beams of these size being off of the ground this high. Rebar enforced concrete foundation will put up against flood waters better than wood foundation as long as it is in soils than will drain well and won’t settle after each flood event. The soil type is a major factor when determining foundation construction. The site is mostly a Hayden Loam composition (Web Soil Survey) which drains well and requires to go further than 80 inches deep for foundation footings to be sturdy. This site is well suited for the proposed concrete foundation.
PROJECT DESCRIPTION Once I verified the materials I was going to use through research, I needed to first work with the contour data to regrade the site to build access to the top of bridge (T.O.B.). My goal is to create a ramp that is easily accessible with a small utility vehicle while staying ADA compliant. In order to hold the weight of a utility vehicle while staying inside the standard distance between the centers of beams, the design details four GLULAM beams than span 46’ with a 28.5” depth each.
Weight Capacity of Beam per Linear Foot
[6’ 5/8” (beam O.C.) ÷ 4 (number of beams)] ÷ [46’ (span)] = 295.6’ [295.6’ x 110 (design load)] = 32,521 lbs [32,521 ÷ 46’ (span)] = 707 lb/LF PG. 2
The beam calculations made it evident to me that I chose the appropriate decking knowing now that I don’t need joists for this design because the four beams hold enough of my 110 lbs/LF design load. I went with 2”x8”x8’ pressure treated Douglas Fir for its durability and affordability just as the existing bridge has. This creates a surface area of 368 SF (46’ x 8’). The total deck design load is figured by multiplying the area of the deck by the design load (110 lb/SF).
Weight Capacity of Decking
[46’ (span) x 8’ (width)] = 368 SF [368 SF x 110 (design load)] = 40,480 lbs
The railings are where I got to be creative with the materiality by manipulating its form. I wanted a strong connection for the railing, so I made the connection from the beam to the railing directly. I did this without cutting into the 8’ bridge space because I wanted to ensure a vehicle could fit across the bridge. The railing continues to the opposite side of the ramp to ensure a safe passage over the bridge. I specked a 5”x5” weather treated Douglas Fir post spaced 5’ O.C To support the three lateral rails between the posts. To further strengthen the bridge, I added braces between the beams at every spot the post footing made contact to the beam to create 5’ O.C. braces. As I mentioned before, the size of the concrete foundation relies on soil type. The soil on site is said to have a 2,000 lb/SF soil bearing capacity. I need to find how much my foundation is carrying to know how big the foundation needs to be.
Weight Capacity of Foundations [1.5’ (depth) x 8’ (width) x 5.5’ (height)] = 66 CF [66 CF x 110 (design load)] = 7,260 lb per foundation [7,260 lb ÷ 2,000 (soil bearing capacity)] = 3.63 lbs per foundation
PROJECT REFLECTION Overall, this was a challenging project. There was a lot of referencing and researching at the base of this, but I do think the process of construction documents has clicked. I know what I need to work on and I will feel comfortable doing these in the future.
PG. 3
COVER PAGE
SCALE: 1’=1/8”
1a
COMPONENT: DECKING
(74boards)
1b
SCALE: 1’=1/5”
COMPONENT: HAND RAIL
(5’O.C.)
SCALE: 1’=1/5”
FINAL PROJECT: DOCUMENTING THE DETAIL: A BRIDGE LANDSCAPE ARCHITECTURE 481 FALL 2017 COLLEGE OF DESIGN IOWA STATE UNVIVERSITY INSTRUCTOR: SCHUCKERT
1
AXON
NORTH
DRAWN BY: JEREMY JOHNSON
1210 17 SCALE:
1c
COMPONENT: CONCRETE RAMPS SCALE: 1’=1/5”
(8.3%)
1d
COMPONENT: GLULAM BEAMS SCALE: 1’=1/5”
(4)
1’ = 1/4” DRAWING NO.
1
PLAN VIEW
SCALE: 1”=10’
910
908
909
907 906
909
910
910
BUILT SLOPE
909
909
908
904
908
911
912
RAMP 910
RETAINING WALL
905
T.O.B 913
BRIDGE
T.O.F 911.5
GENERAL NOTES: T.O.F is defined as Top of Foundation.
908 909
909
905 909
381.6 CF of CUT
907 910
906 907 908
T.O.F 909 910 910.5
908 907
SCALE: 1”=20’ 1,040.9 CF of FILL
906
905 909
B
905
CUT AND FILL DIAGRAM
T.O.B 913
T.O.B is defined as Top of Bridge. 912
Top of Ramp is equal to Top of Bridge
RAMP
FINAL PROJECT: DOCUMENTING THE DETAIL: A BRIDGE LANDSCAPE ARCHITECTURE 481 FALL 2017 COLLEGE OF DESIGN IOWA STATE UNVIVERSITY INSTRUCTOR: SCHUCKERT
A
GRADING PLAN
NORTH
912
DRAWN BY:
906
911
912
911
912 905
913 914
BUILT SLOPE
JEREMY JOHNSON
1210 17 SCALE: A 1” = 10’ B 1” = 20’ DRAWING NO.
910
2
ELEVATION & STRIPPED PLAN FACING NORTH EAST
47’
24’
24’
2”X8”TOP RAIL
5”X5”RAIL POST 8.3% CONCRETE RAMP
POURED CONCRETE FOUNDATION
5’
BRACES PER RAIL POST
5 1/8” GLULAM BOARD 28 1/2” DEPTH 46’ SPAN
C
POURED CONCRETE FOOTING
ELEVATION
UNDISTURBED SOIL
5’
GENERAL NOTES:
(see drawing G)
THE FOOTINGS OF ALL BURIED STRUCTURES GO 4’ UNDERGROUND ADDRESSING FROST DEPTH
SCALE: 1”=8’
THERE ARE BRACES FOR EVERY HAND RAIL. THEY ARE SPACED 5’O.C. RETAINING WALL
RETAINING WALL TOP HANDRAIL
2”X8”X8’ DOUGLAS FIR
CONCRETE SLOPE
CONCRETE SLOPE
GLULAM BEAM RETAINING WALL
D
STRIPPED STRUCTURE PLAN SCALE: 1”=8’
FINAL PROJECT: DOCUMENTING THE DETAIL: A BRIDGE LANDSCAPE ARCHITECTURE 481 FALL 2017 COLLEGE OF DESIGN IOWA STATE UNVIVERSITY INSTRUCTOR: SCHUCKERT
DISTURBED SOIL
NORTH
BRACES 5’ O.C. RETAINING WALL
DRAWN BY: JEREMY JOHNSON
1210 17 SCALE: 1” = 8’ DRAWING NO.
3
4’3”
SECTION THROUGH BRIDGE FACING SOUTH EAST
BEAM SEAT
ALL FOOTINGS ARE BUIRED AT LEAST 4’ UNDERGROUND TO SURPASS THE FROST DEPTH AT THIS LATITUDE. THE BEAMS ARE GLUE LAMINATED TIMBER 24” APART AT THEIR CENTERS.
MID RAIL 2”X8”
FOUNDATION
RETAINING WALL
THE ENDS OF THE BRIDGE ARE ACCESSED VIA A SLOPE AND RAMP. RETAINING WALLS HOLD THE EARTH BUILT SLOPE AND MEET AT THE FOUNDATION.
DISTURBED SOIL
1’6”
7 1/4”
8’
UNDISTURBED SOIL
1 1/2”
E
SECTION: BRIDGE AT FOUNDATION
1’ 4 1/2”
1’6 7/8”
RAILS
SCALE: 1’=1/8” DECKING
5 1/8”
2’O.C. 1 1/2”
7.3652
GENERAL NOTES:V BEAMS ARE ATTACHED TO THE FOUNDATION VIA A GLBT HARDWARE CONNECTION SITTING ON A CONCRETE SEAT. BRACES ARE ATTACHED TO THE BEAMS WITH FACTORY WELDED HGB SADDLE HARDWARE PIECES.
BRACE
2’
BRACE HARDWARE
Fc
NORTH
Fb Fa BEAM SEAT
1’6”
FOUNDATION
THESE BRACES CONNECTIONS EACH USE SIX 2.5” DOMED HEAD CARRIAGE BOLTS AND NUTS. BRACES OCCUR AT EACH HANDRAIL SPACED OUT AT 5’.
GLULAM BEAM
FINAL PROJECT: DOCUMENTING THE DETAIL: A BRIDGE LANDSCAPE ARCHITECTURE 481 FALL 2017 COLLEGE OF DESIGN IOWA STATE UNVIVERSITY INSTRUCTOR: SCHUCKERT
GENERAL NOTES:
9’1/4” 8’
F
SECTION: BRIDGE AT BRACES SCALE: 1’=1/4”
DRAWN BY: JEREMY JOHNSON
1210 17 SCALE: E 1’ = 1/8” F 1’ = 1/4” DRAWING NO.
4
SCALE: 1’=1/16”
GLULAM BEAM
GLULAM BEAM
GLBT HARDWARE (2) TWO 2 1/2” DOMED CARRIAGE BOLTS PER SIDE
PRESSURE TREATED DOUGLAS FIR BRACE 5” X 1’6 7/8”
#6 REBAR 12” DEEP
HGB HARDWARE (2) SIX 2.5” DOMED CARRIAGE BOLTS
Fa
DETAIL: BEAM TO FOUNDATION SCALE: 1’=1/16” BEAM CONNECTION
(see Fa)
TOP RAIL
SURFACE
1 1/2” DECK SCREWS FOUR PER DECKING PER BEAM
#4 REBAR
DECKING CONNECTION GLULAM BEAM
RAIL POST
FROST LINE
POURED CONCRETE FOUNDATION
FOUNDATION FOOTING
JEREMY JOHNSON
1210 17 SCALE: 1’ = 1/16” G 1’ = 1/4”
DETAIL: TOP RAIL TO RAIL POST SCALE: 1’=1/16”
KEY JOINT
DRAWN BY:
HGB HARDWARE
Fc
FOUNDATION CAP
DETAIL SECTOINS
Fb
POURED CONCRETE FOUNDATION
FINAL PROJECT: DOCUMENTING THE DETAIL: A BRIDGE LANDSCAPE ARCHITECTURE 481 FALL 2017 COLLEGE OF DESIGN IOWA STATE UNVIVERSITY INSTRUCTOR: SCHUCKERT
DETAIL: BEAM TO BRACE & RAIL POST TO BEAM
G
SECTION: FOUNDATION SCALE: 1’=1/4”
DRAWING NO.
5