بررسي تاثير ناكاملي هندسي اوليه اعضا بر ظرفيت باربري شبكه‌هاي تخت دولايه فضاكار

The Effect of Initial Geometric Imperfection on the Load Bearing Capacity of Double Layer Grid Space Structures

با توجه به اينكه در طبيعت هيچ سازه ايده‌آل كاملي وجود ندارد و كليه سازه‌ها در عمل داراي عيوبي (ناكاملي‌هايي) هرچند جزيي مي باشند، وجود برخي ناكاملي‌هاي هندسي عضوي در سازه‌هاي فضايي تخت دولايه با صدها يا هزاران عضو، تقريباً غير قابل انكار مي‌باشد. اين ناكاملي‌ها موجب افت ظرفيت باربري اجزاي فشاري و در نتيجه باعث افت ظرفيت سازه‌هاي فضاكار مي‌گردد. در اين مقاله دو سازه فضاكار خرپايي مختلف مدلسازي وبصورت غيرخطي براي مقادير مختلف ناكاملي تحليل گشته اند. توزيع ناكاملي ها نيز به دو حالت انجام شده است :1- توزيع يكنواخت 2- توزيع تصادفي. نتايج تحليل ها بصورت منحني هاي بار – تغيير مكان نشان داده شده وبيانگر افت ظرفيت سازه در اثر وجود ناكاملي مي باشد.

The existence of some geometrically imperfect members, like initial curvature in a double layer space structures with hundreds or thousands of members is almost inevitable. These imperfections give rise to loss of load bearing capacity of double layer space structures. To evaluate the effect of initial member imperfection on load bearing capacity of double layer space structures and their failure behavior, two models of double layer space structures were considered and analyzed nonlinearly by different member imperfection values. The distribution of imperfections was carried out in two ways: 1-uniform distribution, 2- random distribution. In uniform distribution one amount of imperfection was considered and performed to all of the members, but in random distributions, different amounts of imperfections were considered and performed to members and then the structure was analyzed. The results of these analyses were presented with load- displacement figures and they showed loss of overall strength of structures due to initial member imperfections, so that the greater amount of initial imperfection led to increase in the loss of strength. With random distribution of imperfections, results showed 17 to 32 percent loss of strength with respect to the normal condition.