Study of edge restraints and localized weakness in the double layer grids of square and rectangular layouts

This research addresses the effect of edge restraints and localized weakness on the structural response of Double Layer Square and rectangular grids in terms of axial forces and deflection. This work is an extension of previous theoretical study done by the authors. It contains the analysis of two double layer grid model structures of 8'x8' and 8'x4' in plan which were modeled and analyzed by using standard SAP90 software under a pressure of 1 psi (145 Mpa) to investigate the stated parameters. Localized weakness problems can occur due to poor connections, heavy concentrated loads, aerial attacks, blasts or due to fire. The grids were braced and loaded at the top chord and supported at supports at the bottom chord. Twelve different edge restraint conditions were studied in terms of deflections and maximum chord forces with a view to suggest some suitable arrangement for temperature and lateral loads which impose opposing nature of support constraints. Three weaknesses in square layouts were considered in maximum moment and maximum shear zones. In rectangular grids two weaknesses were considered for analysis purposes. Dropping the axial stiffness of members in the concerned zone by 60000 times during modeling stages has simulated the localized weakness in both types of layouts analyzed.

Generally by increasing number of supports axial forces and deflections decrease. By removing horizontal restraint at supports for avoiding temperature stresses, vertical deflection increases. For square layouts if the weakness occurs in peripheral zone it becomes critical which might be taken care of by central stiffness arrangements .For rectangular layouts, weakness at the centre is critical for which again stiffening of central portion may be useful.

• INTRODUCTION

• STUDY OF EDGE RESTRAINTS

• STUDY OF LOCALIZED WEAKNESS

• STRUCTURAL MODELING

• CONCLUSIONS

• ACKNOWLEDGEMENTS

• REFERENCES