Yêu cầu cơ bản quan trọng nhất của kết cấu xây dựng cũng như cơ kết cấu là hệ chịu lực phải nằm trong trạng thái cân bằng ổn định. Một phần quan trọng trong kết cấu xây dựng là mô hình hóa hệ chịu lực mẫu từ công trình xây dựng phức tạp (ngôn ngữ trong ngành còn gọi là "bổ kết cấu") làm sao để làm sao tính toán được trong giới hạn công sức hợp lý kinh tế. | APPROXIMATE THEORY FOR LATERAL LOAD ANALYSIS OF WALLS SUBJECTED TO PRECOMPRESSION WITH AND WiThOUT returns Wall without returns Having taken into consideration all the factors contributing to the lateral strength of the wall an approximate analysis Hendry et al. 1971 can be developed based on the following assumptions Elastic deflections of the wall supports are negligible. Failure occurs by horizontal cracking at the top centre and bottom of the wall causing rotation about horizontal lines through A B and C Fig. . The forces acting on the top half of the wall at the point of failure are shown in Fig. . By taking moments about A ơtL t-a qoh í 0 8o-í f-a ỉ2 where ơ precompressive stress t thickness of the wall which is subject to precompression in the case of a cavity wall with inner leaf loaded thickness should be equal to the thickness of inner leaf only L length of wall fr height of wall 0 transverse or lateral pressure and a horizontal distance through which centre of the wall has moved. If the compressive stress is assumed constant throughout the uplift of the wall at failure the maximum pressure resisted by the wall is equal to qữ 8ơt2 h2 when d 0 If the precompression increases on the wall with uplift of the building as explained above it is possible for the moment of resistance ơtL t-a to increase even though the moment arm t-a decreases thus resulting in an increase in the maximum lateral pressure resisted by the wall. Wall with returns In the case of a wall with returns part of the lateral pressure is transmitted to the return thus causing axial and bending stresses in the return. 2004 Taylor Francis Fig. Simplified failure mechanism for walls with returns. Now substituting the value of q0 wall with no return from equation into equation 1 _ - l-l 3at Similarly for a wall with two returns Fig. a hL ơt L fcy h h2 1h r Í2 8 T 8ơt2 1 1 2 30 where a L lí From equation 1 i 2 - q 1-2 3 a .
