Things need to consider in trusses inspection for civil and structural engineer

When the design of prefabricate trusses have been approved. It will under go fabrication in factory. Upon completion of fabrication of trusses, it will deliver to site for construction. As a civil and structural engineer, one of the duty of engineer is to inspect the trusses.

Engineer has to make sure the design of trusses (theory) has been properly transfer into actual product.

When trusses deliver to site, site agent or engineer needs to verify the quality of timber product. Timber has to be treated to avoid attack by termites. Normally the color of pressure treated wood is in green color. Moreover, whenever a section of timber is being cut, it will show that the green color chemical will penetrate from surface of timber into it. Certificate of treated timber must be obtained from supplier for record purpose.

Then timber trusses have to check on the timber defect such as rotten timber, damage timber. Any defect found must be rejected immediately. Such check mainly by visual inspection. In found any suspect member, engineer can request for sample testing to any approved laboratory.

Further from what mention above, engineer needs to check the timber sizes. It to ensure that the sizes provided are according to trusses design sizes. This can carry out by using measuring tape. Sometime, it is impossible to insect every single item of timber. Therefore, engineer has to use based on his best knowledge to has randomly sampling inspection. One of the way is to inspection on the critical trusses.

Whenever, the connection of trusses is done by bolts and nuts. First, engineer must visually inspection the bolt holes. It is common that contractor simply open the hole for bolting, until sometime the hole just at side of timber member such as 5-10mm from edge of member. This hole will easy loosen out from timber and affect the integrity of timber truss structure. The position of bolt holes on timber is important. It must according to truss design.

Before erection of trusses to roof structure such as roof beams, the level of roof beams has to adjust to allow trusses to rest on roof beams. Inconsistency of roof level has to avoid.

After the trusses have been erected up to roof structure, engineer must ensure that the vertically of trusses have been achieved. Position of trusses must according to design drawing. Further more, the supports of trusses must according to design drawing. As for example, if a truss has four supports, engineer has to ensure that these four supports have been installed. It to make sure that the roof loading behavior has not been changed. If  roof level is inconsistency for roof truss; in order to achieve supports condition, some irresponsible contractor will use small element such as broken timber to slot between timber truss and roof structure. It is not a permanent structure. The broken timber will drop off some days after the truss erection. 

Connection of truss to truss must has special precaution. It has to proper connected by using MS plate or other proper structure and nailing has to avoid.

Any change in timber structure arrangement has to under go design work. Do not allow any modification of trusses without approval from design office.

If there are some dispute at site cannot be resolved, try to work it out at office. When contractor at site do not want to follow engineer instruction, DO NOT argue with them. It may end up with quarrel; sometime with fighting. Therefore, leave the site immediately. Later put in writing and send to them.