6 



Design of Laminates 



The efficient and economical utilization of construction materials and the selection of 

 the appropriate material for specific applications can only be accomplished by knowledge of 

 the behavior of available materials and associated design theories. This Chapter presents 

 fundamental structural principles and theories as guidance for designing with fiberglass re- 

 inforced plastics. The utilization of these materials does not require any new principles of 

 design but certain principles assume greater importance and require more extended con- 

 sideration when designing for fiberglass reinforced plastics. Changes in the design pro- 

 cedures and theories presented will probably occur with increased design experience and 

 when complete technical data as to the behavior of these materials becomes available. 



Some of the design data developed, particularly tables and graphs associated with 

 compressive strengths, plates, stiffener and plate combinations and sandwich construction, 

 although considered theoretically sound, have not been completely verified by detail labora- 

 tory tests, but have proven satisfactory in some limited applications. Therefore careful 

 interpretation of these data should be made. 



Factors affecting the strength of fiberglass reinforced plastics as discussed in Chapter 5 

 are not considered in the design procedures presented here since they are not functions of 

 the basic design principles and theories. These factors however should not be ignored and 

 proper allowances should be provided when necessary. They should be separately considered 

 for each application and adequately allowed for in the selection of the factors of safety. 



The physical properties values for the various types of reinforcements used in the 

 design examples are values given in Tables 5-6 to 5-14. These values have been selected 

 at random to demonstrate the suggested methods of analyses. The higher values in the 

 tables should only be used when justified with necessary strength tests of the actual produc- 

 tion laminate to be used. 



BEHAVIOR OF LAMINATES 



Fiberglass laminates are composed mainly of two materials, fiberglass reinforcement 

 and resin. A laminate is similar to reinforced concrete with the exception that the fibers 

 are distributed throughout the entire laminate and occupy a greater volume than does the 

 steel in reinforced concrete. In the fiberglass laminate the glass and resin are assumed to 

 act as a unit for all combinations of stresses, whereas in reinforced concrete the steel acts 

 principally to resist tension while the concrete resists compression. This implies that for 

 any loading condition, both the resin and the fiberglass reinforcement are firmly bonded 

 together and undergo equal deformations. 



6-1 



