Case Studies

3 Stacked Roof Trusses for Clubhouse in Pinehurst N.C.

See photo under Pre-Assembly section. .   Web compression bracing had to be braced to the building walls and roof deck

Permanent “X” bracing was installed to prevent racking from wind loads on the 36 foot tall roof.

Temporary bracing was installed for the erection process and remained to act as the permanent bracing.  Preassembly was used thus leaving a preponderance of bracing in the system.

Wood Roof Truss Collapse in Charlotte N.C.

Engineer of record required an onsite truss erection meeting with the erector and truss manufacturer.   Engineer required that a copy of HIB-91 be available on the site.    Meeting confirmed that the erector had experience erecting 63 foot long scissor trusses.

Engineer of record plans called for the trusses to be fabricated out of Southern Yellow Pine lumber.  Truss manufacturer used machine graded Spruce Pine Fir.

Roof trusses collapses after 19 trusses were placed on the braced metal stud walls.  The walls did not move.

Erector claimed that the trusses were much more flexible than what he was used to using. 

Erector used 2 foot long lumber to brace from one truss to the adjacent truss.  All trusses were spaced 24” o.c.  Erector had 3 rows of bracing of the top chord on each side of the ridge.  

A review of the buckling equations indicated that the SYP at E = 1.6 and SPF at 1.1 would have required about 40% more bracing of the top chord than the erector applied.

During interview with the erector he stated that he installs 14 foot bracing (permanent) after the crane leaves the job site.   The erector’s contract was for only the truss erector labor and crane bill.

Wood Roof Truss Collapse in Wilson  N.C.

The church members installed 60ft + scissor trusses and the trusses collapsed.  New trusses were provided by the manufacture, and again the trusses collapses when installed by the church members.  The manufacturer provided another set of truss and an installer.  The installed successfully installed the scissor trusses with 3 times the bracing that the church members utilized.

76 Foot Long Roof Trusses

One day, the crew did not show up for work.  The three guys on the site were 60+, 55+ and 45+ years old.   They lifted each truss with a spreader bar.  Set the 76 foot long truss into the jig.  Then pre-assembled 5 trusses together.   Then they repeated the process all day.   Two days later the trusses were erected with the crane and the old (three wise men) guys tied the trusses to the steel using butler scaffolds.  A “J hook” lifting system and special setting techniques were used in this process.

Wood Roof Truss Collapse in Benson  N.C.

Again, 63 foot long scissor trusses were ALL INSTALLED ON THE BUILDING.  Plywood roof sheathing was installed on the east side of the ridge – 100%.   Everyone went home of Friday.  Rain did occur over the weekend.  The subcontractor showed up on Monday morning and found the building was standing.   The sub drove ½ mile down the street to get coffee, when they came back the building had collapsed.

Engineering investigation indicated that the west side of the ridge had only 2 runs of top chord bracing.  Engineering calculations indicated that installing the plywood roof sheathing on one side did not have an adverse effect of the truss bracing.

A roof truss bracing plan was designed, the new trusses were installed.  Halfway through the installation, the 14’ tall metal stud walls began to rip out the diagonal wall bracing. 

A review of the building plans showed an architect seal only.  No engineer was involved in creating the structural plans.  The wall section was found to have been designed by an employee of the General Contractor who had cadd experience.  Pilasters were added to the exterior of the wall to brace the loads from the scissor trusses. Special Simpson clips should be used in this case.