Bowstring Truss Report.docx

ADV. CONSTRUCTION

TIMBER BOWSTRING ARCH TRUSS INTRODUCTION •

Timber Bow trusses was a popular structural system in the early 20th century, especially in America. They consist of an arched beam above and a straight beam below.

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This engineering feature has historically been popular both for bridges and for industrial architecture such as hangars due to its ability to clear-span large distances.

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All bowstring trusses are not created equal and do not share the same characteristics when found in a building and occupancy. They may have the same shape, but shape alone does not define the bowstring truss.

SHORT LENGTH TIMBER 

Short length timber is available in the size of 1-2 M.

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It is thoroughly seasoned wood-work that has undergone chemical preservation as well as prevention of decay of the construction material.

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SLT requires simple but special nailing and fastening techniques and joining methods.

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Advantage of SLT is that it has a good salvage and reselling value.

LARGE SPAN STRUCTURES •

Large Span Structures are the structures where the span exceeds 12 meters.

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It is used where large floor area is required free of roof support columns.

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SLTs are weak to be used in large span structures so we are gluing SLT members in a staggered laminated form.

PURPOSE AND USES •

Bowstring arch truss roof creates unobstructed, column free spaces greater than 30 meters and is used for variety of functions.

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These include activities where visibility is important for large audience.

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This type of truss is also used where flexibility is important and where large movable objects are housed.

BOWSTRING ARCH TRUSS BRIDGE

BOWSTRING ARCH TRUSS

ADVANTAGES OF TIMBER BOWSTRING ARCH TRUSS •

Bowstring trusses are great for spanning large distances- thousands of bowstring trusses were used during World War- II for holding up the curved roofs of aircraft hangars and other military buildings.

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Roofs built over Bowstring Trusses have no need to cap the ridge at the top of the roof, saving time and money in the construction process.

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A Bowstring Truss may be built to provide the appearance of either a flat or a pitched truss and thus is probably the most flexible of all the truss types.

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These structures lend themselves to new uses because their spans allow for large skylights and flexible spaces.

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Arch in the shape of a parabola is theoretically the most efficient because direct stress alone is developed in the arch and in the tie member.

DISADVANTAGES OF TIMBER BOWSTRING ARCH TRUSS •

Timber is now out-dated and mostly steel Bowstring Arch Trusses are used.

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Bottom chord fractures and splits can be encountered on Bowstring Trusses.

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Buildings with bowstring truss roofs will not only collapse downwards, but can also force the load- bearing walls, upon which the truss sits, outwards in a collapse situation.

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Wood truss members are compromised by water leaks, due to lack of maintenance or by the construction methods used in erecting masonry supporting walls.

EFFECTS OF WEATHER •

The curved top chord allows the buildup of snow and water weight on the roof to cause uneven loading, increasing the stress on the wood members. In turn, the uneven loading can reverse the stress on the wood members causing a “Push-Pull” situation that weakens the wood joints.

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Corrosion on the nails installed on the top chord piles is an indication of prolonged moisture exposure from roof leaks.

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Repeated exposure to moisture also affects fastener capacity.

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Wood has a high tendency to rot due to presence of moisture.

PROCESS OF CONSTRUCTION • STEP 1: Lay out the pieces of the arch and fix it together on the ground.

• STEP 2 : Erect the columns.

• STEP 3 : With the help of cranes, the arches are raised and placed on the top of the columns and fixed.

• STEP 4 : Formwork is used to provide support to the arches.

• STEP 5 : Finally purlins are attached and fixed in position.

KEY PLAN

60 X 30 M KEY ELEVATION

SPAN- 30M POST HEIGHT- 6M POST CROSS SECTION – 900 X 900 mm HIGHEST LENGTH OF THE STRUT – 3M

JOINERY DETAILS  Detail at A

 Detail at B

 Detail at C

 Detail at D

The gusset plate is placed between the struts and arches and is bolted.

Struts- 100 X 300 mm Arches – 200 X 400 mm

 Foundation Detail

MODEL

SUBMITTED BY: • • • • • • • • • • •

AMRITHA M. B. NEHA SHARMA SNEHA ELUGAM KAKOLI BORAH NIKITA LAKRA P. SUBHASHINI SHIVANI JAISWAL SHREYOSI DHALI SNEHA NALLAGONDA SNEHA CHAVAN SUPRIYA SHAH

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