Analysis of Trusses in Raymond Great Hall

 

University of the Pacific

Stockton campus

Stephen Morse & Steven Granados

 

Purpose

The truss analyzed in this project was designed to be one of many to support the roof in the Raymond Great Hall on the Stockton campus of University of the Pacific.  The purpose of this analysis is to discover the forces present in the members of the truss under normal conditions, and to determine the maximum tensile and compressive forces to which the truss members will be subjected under such loads as may be caused by various extreme weather conditions.  It is not within the scope of this report to determine whether the truss will be sufficiently strong to support such loads. 

 

Assumptions

Due to the unavailability of the original construction plans for the Raymond Great Hall, a number of assumptions were necessarily made in order to proceed with the afore-stated analysis. 

 

  1. The roof was assumed to be a uniformly distributed load over the entire top surface of the truss, and was modeled as such in the free body diagrams and for the calculation of the forces in each of its members. 
  2. The weight of the roof was modeled in two ways:  first, during the calculation of the forces in the lower members of the truss, it was modeled as a discrete force acting perpendicular to and in the center of member ABC.  For the calculation of the forces in members AB and BC, the weight of the roof was modeled as three discrete forces applied at points A, B, and C.  The magnitudes of these forces were determined algebraically.  (See calculations.)
  3. The weight of the roof (denoted in calculations as “R lb/ft”) and the hanging lights (denoted in calculations as “L”) were left as variables for the general calculations.  Different values for the weight of the roof, based on varied construction techniques and materials selections, will be applied to the equations obtained to yield possible internal forces for the truss. 
  4. The weights of the beams within the truss were ignored as an approximation to simplify calculations.  A complete analysis would require this to be taken into account, but would be extremely difficult without the aid of computer modeling. 
  5. The lengths of the beams were estimated as carefully as possible from the safety of the ground. 
  6. One truss was estimated to support the weight of fifteen (15) linear feet of roof. 

 

History

Raymond Great Hall was constructed in 1962 as part of the Raymond “Cluster” College Complex.  It was built over the section of the University of the Pacific campus previously occupied by Baxter Stadium.  The Hall was dedicated on October 13, 1962.  It was built in the style of Modernistic English Georgian Architecture, which utilizes unfinished wood beams to create the exposed trusses that support the high, vaulted, barn-like ceiling. 

 

Materials and Methods

The seven (7) inch square beams of which the trusses are comprised are held together with large steel gusset plates and steel bolts.  The beams are sealed with an undetermined compound to protect against water and insect damage.  The architect selected wood beams for their aesthetic virtues as well as their cost effectiveness.  Without the original construction drawings and detailing, which are believed to be held in the City of Stockton archives, some of the actual construction methods and techniques cannot be determined.  Such information, however, is not vital to the scope of this report. 

 

Calculations

The methods of joints and sections were used in the analysis of the forces present in the truss members.  The forces present in each member are as follows, noting that forces with a positive magnitude imply that the member is in tension, and forces with a negative magnitude imply compression.  “R” represents the uniformly distributed weight of the roof, and was calculated to be 126.5 lb per linear foot.  “L” represents the weight of the lights hanging from points J and H, which were assumed to weigh 70 lb each.  Note also that there are no zero force members in the truss.  The complete calculations may be viewed here. (page1)(page2)

 

AB = -41.500R – 3.607L

BC = -37.865R – 0.698L

CD = -51.440R – 3.487L

AJ  = 27.033R + 3.113L

JI   = 16.703R + 1.908L

CI  = 24.090R + 1.908L

BJ = -10.005R – 1.185L

JC = 7.948R + 1.942L

DI  = -6R

 

Conclusion

Under normal conditions, member AJ is subjected to the maximum tensile force, and member CD is subjected to the maximum compressive force, their magnitudes being 3637 lb and 6751 lb respectively.  Assuming the steel gusset joints are able to withstand larger forces than the beams, members AJ and CD are the anticipated failure points of the truss.  Under special loading conditions such as may be possible in extreme weather, the magnitude of the forces in these two members could more than double. 

 

In the case of a heavy rain, 0.25 inch of water is taken to be standing uniformly distributed over the entire roof.  This contributes 1128 lb to the overall weight, bringing “R” up to 146.0 lb per linear foot.  A heavy snow (which is highly unlikely in Stockton) could contribute five thousand pounds or more to the roof’s overall weight!  For the purpose of these calculations, the snow was assumed to be 10% water by volume (fairly dry; also unlikely in Stockton) and to have formed a one-foot thick layer uniformly distributed over the roof.  This contributes 5413 lb, bringing the distributed load up to 220.1 lb per linear foot, and making the forces in members AJ and CD 6168 lb and 11566 lb respectively! 

 

Link to Powerpoint Presentation

 

References

Professor Jeff Burmeister

Don Walker, UOP library archivist and historian

UOP physical plant

Pacific Weekly newspaper (library archives)

Photo file on Raymond College (library archives)

CSAC:  http://www.csac.org/Education/glossary/density.html

PSC Roofing Tiles:  http://www.pragatisales.com/roofing_tiles.htm

Bob Vila Home Improvement Website: http://www.bobvila.com/HowTo/TipLibrary/Subject/Carpentry/Engineered_Wood/0389-Plywood_Weight.html