Effects of Modeling Assumptions on Lateral Load Distribution in Low-Rise Timber Buildings

摘要

This report presents an analytic model to determine lateral load distribution in low - rise timber buildings. Modeling effects are considered for different building plan length - to - width ratios, floor joist and wall stud stiffness, floor and roof diaphragm stiffness, study to still and plate connection fixity, and assumed length of windward wall contributing to the middle and end frames. Load distributions based on two and three-dimensional analyses are compared to the tributary area method for balloon and platform constructions. The building model is a three - story symmetric structure of standard construction with 2 by 4-inch studs spaced at 24 inches and no interior partitions. Plywood wall, floor, and roof sheathing have nails spaced at 6 inches. Conventional roof trusses spanning the width of the building are 24 inches on center. The results show that the component interaction represented by joint stiffness is the predominant influence in how the load is distributed and that component stiffness is a secondary factor. The effects of building length - to - width ratio, varying floor and roof diaphragm stiffness, and assumed length of windward wall contributory area to middle and end frames are minimal in a three - dimensional analysis using this model. For platform or balloon construction, the end - racking walls can be designed based on loads supplied by the tributary area method. The percentage of lateral windload distributed to end walls is primarily influenced by the relative top and bottom fixity of the vertical members, and thus the paper recommends two - dimensional analysis if interior partitions are neglected. References, tables, graphs, and diagrams are supplied. (Author abstract modified).