Optimization Design Research Of Reinforced Concrete Frame Structure With Haunch Braces

The reinforced concrete (RC) frame structure with haunch braces is a new kind of long span frame structure. The force transferring mechanism of normal RC frame structure can be changed by adding haunch braces. In recent years, steel frame structure strengthened with haunch braces are researched and applied in the foreign seismic rehabilitation. However, the performances of RC frame structures with haunch braces have rarely been reported. Comparing with the normal RC frame structures, the loading capacity of the RC frame structure with haunch braces is significantly different. In order to promote the practical application of the new kind of RC frame structure with haunch braces, based on the practical project, the basic loading performances and the earthquake resistant capacity of the new kind of structure system are deeply investigated from experimental test, numerical simulation and practical monitor in this paper. The research is related to provide a good basis for the future study. The main works and conclusions include as follows.1. The effects of the located position of haunch braces on the displacement and the internal force and reinforced of RC frame structure with haunch braces are analyzed using professional structural analysis and design software PKPM. The results indicate that rational interval angle of the haunch brace and the beam is about 30o~50o, and rational horizontal span of haunch brace is about L/10~L/6. It is beneficial to increase the interval angle of the haunch brace and the beam. But the constraint of the shear-span ratio and the axial compression ratio for the seismic design of frame column must be taken into account when the vertical height of haunch brace is determined.2. One 1:4 scale RC frame structure with haunch braces are tested to study the basic loading performances and the failure mechanism under the vertical and horizontal loads. The characteristic of the skeleton curve is discussed, ductility and stiffness variation. The main experimental results are as follows. (1) Under the vertical action, the intersection sections of frame beam-haunch braces firstly reaches yield. With increasing the vertical load,the bottom reinforcement strain of mid-beam increases rapidly and reaches yield strain. The reinforcement strains of the intersection sections of frame column-haunch braces are larger than those of the column base sections, and which increase more rapidly. The dangerous sections of the frame beam are located in the mid-span and the intersections of beam-haunch braces, and the dangerous sections of the frame column are located in the intersection of column-haunch braces. (2) Under the horizontal action, the dangerous sections are respectively the column base and the intersection of beam-haunch braces. Many bending-shear diagonal cracks are located in the intersection of column-haunch braces, and flexural deformation is apparent. The skeleton curve of specimens generally experience three stages, such as elastic, elastic-plastic and plastic stages, and which shows a good deformation. (3) No matter whether the vertical load or the horizontal load, cracks of beam end, column cap and joint zone are relatively not many, and strains in longitudinal steel and stirrup are also relatively small. This shows that haunch braces improve the mechanical behavior of joint zone and the requirement of strong joint is easily achieved. (4) Effective length of frame beam and column is shortened, especially the shear-span ratio is strongly decreased owing to the haunch braces.3. According to the experimental, numerical simulation and practical monitor results, the key technical measures of structural design for RC frame structure with haunch braces are summarized in this paper. The main measures include such as the application scope, the seismic fortification grade, the earthquake action, the selection of structural material, the structural analysis, the located position of haunch braces and the section optimization, the construction requirements of structural member and joint, etc.. Finally, the design and construction monitoring of a practical project is described.