Gathering Haunch Design Data by Photoelasticity PDF Download

Author: Richard B. Heagler
Publisher:
ISBN:
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Languages : en
Pages : 0

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Book Description
"The haunching of beams and columns and the haunching of rigid frames is performed by design engineers for the purpose of relieving stress concentrations that might occur at discontinuities in structures. The haunch performs this relieving of stress concentration by increasing the rigidity of the structure at regions of high stress. Usually this design step is one of trial and error; that is, the engineer will select a haunch or method of haunching and then check to see if the result is sufficient for his purpose. This can be a time consuming process and can lead to uneconomical design. In the area of reinforced concrete design the engineer is faced with the decision of how much reinforcement is required and where he must place it for optimum performance. Many times he is forced to design on an intuitive basis. The specific problem to be treated in this study is the partial stress analysis of the basic beam and column arrangement shown in figure 1-a. This basic arrangement is varied by the addition of haunches as is shown in figures, 1-b, 1-c, 1-d, 1-e, and 1-f. The column-beam arrangement is loaded as is shown in figure 2. All arrangements are loaded in this manner for this study. The column has deliberately been kept short so as to eliminate the possibility of a bucking failure. The beam has been made shallow so that fairly high bending stresses will be present under load. As can be seen from figure 2 the stresses that will be present under the applied loading will be caused by the high shear in the beam at the column face and by tensile and compressive stresses in the beam caused by bending and by the bearing stress on the beam (or column) at the intersection of the beam and column. It is evident then, that the haunch will not act as just a part of the beam, nor will it act as just a part of the column, but will tend to be a part of both. The action of the haunch then may be considered to be a "stress bridge" between the beam and column, allowing and helping them to act as a unit in withstanding the applied loads. The stresses that the haunch will be subjected to are not obvious and the shear stresses in the beam are not obvious. The primary function of the haunch would be to reduce the shear stress in the beam by increasing the area over which the shearing force acts. The purpose of this study is to gather basic data on the performance of haunches as stress relievers and to obtain information that may be useful in the design of haunched members. A knowledge of the stress condition would also be applicable to a concrete structure. If the directions and magnitudes of the stresses were known, then reinforcement could be placed accordingly. The photoelastic method of stress analysis is one way in which the problem could be approached. This method will allow the visual observation of the shear stresses that will be present in the haunch. Regions of high stress then can readily be seen. With a few fairly simple calculations (which will be shown later) the normal stresses could also be found and dimensional changes in the haunch then might be made or reinforcement placed to withstand the stresses that may be present. Other methods of analysis would also be applicable. A model could be built and strain gages could be applied. However, in order to get a picture of the overall stress pattern many strain gages and many models would be needed for the investigation. The photoelastic method provides an overall view of the stresses and the models used can be made easily and quickly with a minimum of expense"--Introduction and statement of problem--leaves 2-4