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Instruction Manual

Table of Contents

TOC o “1-3” h z u Introduction PAGEREF _Toc369809257 h 3Prose PAGEREF _Toc369809258 h 3Characteristics of a wooden truss PAGEREF _Toc369809259 h 3Materials PAGEREF _Toc369809260 h 4The step-by-step construction process PAGEREF _Toc369809261 h 4Truss specifications PAGEREF _Toc369809262 h 7Loading conditions PAGEREF _Toc369809263 h 8Risk assessment PAGEREF _Toc369809264 h 8Conclusion PAGEREF _Toc369809265 h 9Work Cited PAGEREF _Toc369809266 h 10Appendices PAGEREF _Toc369809267 h 11Appendix I: Roof dead loads PAGEREF _Toc369809268 h 11Appendix II: Shapes and sizes of common trusses used in construction industries PAGEREF _Toc369809269 h 12Appendix III: Modification factor for duration loads on timber PAGEREF _Toc369809270 h 12Appendix IV: Truss deflection specifications PAGEREF _Toc369809271 h 13

List of figures

Figure 1: Basic wooden truss members ……………………………………………………….….5

Figure 2: A representation of a truss under the compression and tension forces………………….6

IntroductionThe following discussion focuses on the steps followed while constructing a truss for bridge. Trusses perform important tasks in supporting the roofing of any building and as such require specific instructions while constructing them. A truss could be described a framework of materials acting primarily in compression and tension. Being light in weight, a truss is a very stiff form of construction and that is the reason why it is used in construction. Wooden trusses the most common types used in building and construction industry today because they are cheap and requires less labor and experience to construct (MiTek 3). Roofing materials are designed to support various building loads as shown on appendix I. In addition, trusses come in various shapes and sizes as shown on appendix II.

Prose

Characteristics of a wooden trussThe use of wooden trusses is increasing globally because they near the following advantages:

Strength: A wooden truss provides a strong and efficient framework

Economy: Efficient use of wood and the provision of a system that can be easily installed during construction it the most economical roofing framework

Versatile: wooden trusses easily accommodate various designs used in the construction industry. Its versatility makes it a perfect roofing material in hybrid construction where they are used with steel, concrete or brick walls.

Environment: Wood is the only renewable building material and this makes it posses various environmental advantages. It optimizes wood use for specific applications.

MaterialsIn selecting any material, it is necessary to put into consideration a number of factors including cost, performance, safety and regulation. The following materials are needed during the construction of a wooden roofing truss.

Wood

Truss plates

Nails

Hammer (claw hammer)

Tape measure

Marking pen

Saw (cross saw and tenon saw)

The step-by-step construction processStep I: A research should be conducted to ensure that the designed truss suits the project or building. In addition, the truss should not violate local and international codes. Moreover, it should be designed to meet wind load, snow load and any other load associated with building structures. Figure 1 shows basic truss members

Figure 1: Basic wooden truss members

Step 2: Truss design

The selected truss design should suit the building.

Measure and cut materials for a truss using the recommended measurements taking into accounts allowances.fit the pieces together using nails and using correct dimensions. All connections should be tightly fitted

Select the best quality for top cord and the bottom cord. These areas bear the highest stress. Figure 2 shows various forces acting on a bridge that an engineer should consider while making a design.

Figure 2: A representation of a truss under the compression and tension forces.

Nail all truss connections on a solid, level ground. Nails must penetrate all gussets and plates

The amount of load that a timber can sustain for a given period is determined using the modification factor table shown on appendix III.

Step 3: select appropriate lumber for the truss

Softwoods are most preferred for making lumbers. The following factors are considered while selecting the lumber for a truss;

Size of the lumber

Quality of the lumber

Straightness

It should be kiln dried because green lumber shrinks or warps after the truss is assembled

Step 5: The bottom chord board is placed with the crown up. Scribe lines where cuts will go through.

The size/shape of a wood truss is requires that some field assembly be done. The installer should ensure proper field assembly is done. In addition, the building component safety lists all details that guide a field installer on how to place a truss on the wall.

Step 6: Fixing on the building

Trusses to be located on the edge at every 10 feet along the floor

They should be securely fastened to vertical webs. Blocking behind the vertical web is recommended to enable nailing

Special engineering is required for girder floor trusses

Ensure slope for drainage is provided

Cantilever span is controlled by the size of the lumber, the grade and deflection limitations.

Truss specificationsTrusses should follow the following specifications.

Trusses stored horizontally require support to prevent excessive lateral bending and ensure less moisture gain

Brace trusses are stored vertically to prevent tipping

While on uneven ground, trusses should be unloaded to prevent damage

Trusses to be constructed in accordance to Engineering codes and requirements

Always ensure the latest fashion is used

Truss deflection is determined through the specifications shown on appendix IV.

Loading conditionsTimber structures sustain a much greater load for a shorter period compared to their metal counterparts. The loading condition for timber trusses are as follows:

Long term: These are made up of loads on the top chord and dead in addition to permanently imposed loads.

Medium-term: consists of long-term loads plus the imposed top chord loading.

Short-term: Consists of medium loads and an addition 900N man load modified depending on the regional standards (MiTek 5-11).

Risk assessmentThe design process of in the construction industry has inherent risks. Therefore, cost estimation occurs through formulation of assumptions, which have room for future alteration. Possible risks, which may affect the project, include changes in weather during the construction process and conditions of the ground on which the project construction takes place. Another risk source would be the promoter of the project who may alter the designs to align them with the technological advancements. As such, risk identification in civil engineering process is a crucial step to forecast the success of the project. However, the identified risks need effective management to ensure that they do not lead to creating inefficiency in the project life cycle. Civil engineering structures construction occurs through signing of contracts. These contracts present another form of project risk in terms of disputes and claims inherent within these contracts ((Woodward 97-103).

Conclusion

Trusses are the most commonly used roof supporting materials in most house construction works today. Engineers should ensure all the designs follow the above procedures and standards in order to ensure production of high quality truss. The above manual would be most appropriate in all construction works requiring wooden trusses for roofing.

Work CitedMiTek. “Roof & Floor trusses: Design Information, Technical Data, Approvals, specifications and Details”. A Manual for Architect and Engineers, 2012. Web:

http://www.mii.com/artefact/download.asp?aid=48639Woodward, J. Construction Project Management: Getting It Right First Time.

Business & Economics. Thomas Telford. 1997.

AppendicesAppendix I: Roof dead loads

Appendix II: Shapes and sizes of common trusses used in construction industries

Appendix III: Modification factor for duration loads on timber

Appendix IV: Truss deflection specificationsMaximum depth Span/24 Inches

Maximum deflection Span/240 (live load)

Recommended camber Dead load deflection