Why Are Some Design Choices Better than Others?

A handful of design managers chimed in during the design sessions at BCMC: they’re starting to see more differential deflection specifications in plans. That’s great, because then their designers can account for that aspect of truss design when bidding for jobs.

 

There’s still a problem, though: what to do with the 90% of jobs that don’t include differential, or relative, deflection in the specifications. If no differential deflection is specified, do you design for it? If you design for it and your compe-tition doesn’t, are you pricing yourself out of the job?

 

This question does not have a definitive answer. Clearly, differential deflection is much more of an issue for floor systems than for roofs, because a homeowner has an immediate reaction to walking on a floor where one truss flex-es and the next does not. Yet because differential deflection is a performance issue rather than a structural issue, it’s both more noticeable and less regulated than other aspects of design. For example, there are currently few guide-lines in ANSI/TPI 1-2014 or in building codes.

 

Morris and LaBlance shared their insights and walked the audience through a variety of specific scenarios, pointing out easily missed details and discussing the pros and cons of design choices. They agreed that communication with the customer, as early as possible, is always key to ensuring building owners are satisfied with truss performance.