Stressed Skin Diaphragm Effect Of Portal Frame Structure

In China, with the fast economic development rising, portal frame structures with profiled steel sheets as maintenance system and H type steel members as main frame demostrates great market interests in the field of industrial and civil constructions. It can be concluded from the researches that profiled steel sheet can not only connected with other steel members well, it also has the ability to resist shear force in its own plane; mean while profiled steel sheets can provide supports and torsion restraint to the members with which they connected, so in this way it is benefit to the increment of the stiffness of the whole structure and displacement control. So studis on effect of diaphragram on lightweight steel structures have important values in both theory and engineeing practice.In this paper, geometric nonlinear analysis and comparison using the finite element program ANSYS were made between steel frame structures with diaphragrams and structures without diaphragrams. According to the distribution of stress and the defromation of structures, the effects of diaphragram on steel structures were studied. The main research works of this paper are as follows:(1) According to the code for portal frame structures and standard drawings, several finite element models were built using ANASYS application software. Stressed skin diaphragram structures were generated using two methods. The first is the simplized method proposed by relative literatures; and the second one is the improved method established by this paper according to engineering practice.(2)Based on the two above methods, structures with diaphragram and structures without diaphragram are built respectively. From the comparison of structure stress and deformation, it can be concluded that using different modeling method diaphragram havs great effects on structure stress and deformation.; The improved modeling method yields great value on struture stress and deformation considerablely, while the stress and deformation of diaphragram structures decease a lot. Using improved modeling method, effect of diaphragram can be more clearly shown.(3) Accordin to the result by using improved modeling method, the stress of middle frames decrease while strees of gable frame increase; when taking effect of diaphragram into account, displacement of columns, deflection of beams and rotation of beam-column connections decrease. (4)Parameter analysis such as type of diaphragram, thickness of diaphragrams, slope of frames, slendemess ratio, ratio of rise to span and hollow effect were made. Results show that diaphragram type and position of opening are factors of effect of diaphragram. Effect of diaphragram is amplified with the increase of thickness and decrease of the ratio of rise to span; and damped with decrease of slendemess ratio and slope of frames.(5) Based on method 1 portal frame structure was built and load capacity and deformation were compared after the plastic phase of the model. Parameter analysis such as type of diaphragram, thickness of diaphragram, slope of frames, slendemess ratio, ratio of rise to span and hollow effect were made. Increasing the thickness of diaphragram increases the load capacity of the structures, enhances the ductility and deformation properties of the whole structure. Load capacity of diaphragram structure is amplified with the increase of thickness and decrease of the ratio of rise to span; and damped with decrease of slendemess ratio and slope of frames.