When the design of trusses has been approved from engineer, trusses fabrication will commence. Upon completion of fabrication, trusses will deliver to site for construction. As a civil and structural engineer, one of the duties of engineer is to inspect the trusses.
Engineer has to ensure the trusses has been construction according to design drawing.
After 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 termite. Normally the color of pressure treated wood is in green color. Whenever a section of timber is being cut, it will show that the green color will penetrate into certain depth of timber. Certificate of treated timber must be obtained from timber supplier. It needs 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. The checking on timber is done by visual inspection. Whenever timber quality not to satisfaction, engineer can request for sample testing to any approved laboratory.
Timber sizing is important. Engineer needs to check the timber sizes. It to ensure that the sizes provided are according to trusses design sizes. It can carry out by using measuring tape. Sometime, it is impossible to insect every single item of timber. Therefore, engineer has to base on his best knowledge to have random sampling inspection. One of the ways is to inspection on the critical trusses such as big truss.
Engineer needs to check on trusses connection. There are two types of connection. First is gang nail plate and conventional bolts and nuts. For the later case, engineer must visually inspection the bolt holes. It is common that contractor simply drill holes for bolts. Unfortunately, some inexperience contractor drills the hole just near to edge of timber member (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 trusses 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 such as trusses spacing must according to design drawing. Trusses supports are important. As for example, if a truss has four supports, engineer has to ensure that these four supports have been installed. It to ensure that roof loading has been transferred to roof structure. If roof level is inconsistency; in order to achieve supports condition for truss, some irresponsible contractor will use small element such as broken timber to insert between timber truss and roof structure. It is not a permanent structure. After the trusses have been erected, the broken timber will be loosen some days.
Truss to truss connection must has special precaution. Trusses have to connect by using MS plate or other proper structure. Nailing has to avoid in trusses.
Any change in timber structure arrangement need to has attention of designer. Do not allow any modification of trusses without approval from design office.
Whenever there is some dispute at site cannot be resolved, try to work it out at office. If contractor at site do not want to follow engineer instruction, do not argue with contractor. Else it may end up with quarrel; sometime with fighting. Therefore, leave the site immediately.