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The design of the number of studs and layout of the studs along a member is done for the current cross-section that exists in the model at the time the form is run.
Before any attempt to position the studs along the composite member, the program first determines the number of studs needed in the positive and negative moment regions based on the target degree of composite action.
For the number of studs needed in the positive moment region, the minimum of the compressive strength of the concrete and the compressive strength of the steel section is multiplied by the target degree of composite action, and divided by the shear strength of a single stud. This number is then rounded up to determine the number of studs between zero and maximum positive moment.
For the number of studs needed in the negative moment region, the minimum of the tensile strength of the steel reinforcement and the tensile strength of the steel section is multiplied by the target degree of composite action, and divided by the shear strength of a single stud. This number is then rounded up to determine the number of studs between zero and maximum negative moment.
The program allows studs to be designed in either one or two rows across the width. To allow two rows of studs, set the value of "Number of Rows" in the setup to "2". If two rows are allowed, the program will first check to see if two rows are allowed on the section. Two rows are allowed if the spacing between the studs is greater than or equal to four times the stud diameter, with a distance to the edge of the flange of at least 1 inch or one times the stud diameter, whichever is greater. If two rows can be used, the program will design the studs with two rows only if needed based on the minimum spacing requirements.
For members which are uniformly loaded and have pinned ends, where the moment along the member is positive and the maximum moment occurs at or close to the mid-span, the number of studs needed between zero and maximum moment is doubled to attain the total number of studs. These studs are uniformly distributed along the length of the member. The number of studs will be increased to meet maximum spacing requirements if needed.
Members which either support point loads, such as girders, or have both negative and positive moment, such as fixed-end members, may require an uneven distribution of studs in order to develop the required strength at different locations along the member. To do this, the program divides the member into segments and sub-segments. Any transition from a negative to positive moment, or vice versa, initializes a new segment on the member. Any point load will initialize a new sub-segment within the segment in which it is found.
Members which have a segmented stud layout are also given a uniform stud layout. This uniform layout uses the minimum stud spacing of all segments and sub-segments and determines the number of studs along the entire beam assuming this spacing.
For members with both negative and positive moment, the number of studs in a positive region segment is based directly on the number of studs needed to develop the positive moment capacity from zero to maximum moment as determined by the target degree of composite action. Similarly, the number of studs in the segment for the negative region is based directly on the number of studs needed to develop the negative moment capacity from zero to maximum moment as determined by the target degree of composite action. If the segment is one in which the moment value increases from zero to a maximum moment and then decreases back to zero, the number of studs in the segment is equal to two times the number of studs required from zero to maximum moment.
For members which support point loads, the number of studs needed in each sub-segments is determined by the following equation:
Where:
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Number of studs required in the sub-segment |
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Number of studs required between zero and maximum moment |
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Difference between the maximum and minimum moment in the sub-segment |
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Moment resistance of steel beam alone |
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Moment resistance of the composite beam at the target degree of composite action |
After the number of studs required in each sub-segment has been calculated, the percentage of studs required in each sub-segment relative to the total number of studs required in all sub-segments is used to distribute the studs according to the total number of studs in the segment as determined by the target degree of composite action on the member. This ensures that the total number of studs on the member matches the total number of studs expected according to the degree of composite action. In cases where the member is over-designed, the number of studs in each segment will be greater than required. In cases where the beam size and target degree of composite action have already been optimized, the number of studs in each segment will be equal to or close to the number required.
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