When we look at the Ex section effects in the other models, as in the attached trial model, both elements of the inverted V brace appear to be tensile. The same is true for X crosses. In other combinations, both the diagonals appear tension or both pressure. However, one has to work on pulling and the other with pressure.
Hello there; Since the earthquake calculation is made with the mode combination method, no negative effect is calculated on the structure. First, let's talk about the types of earthquake calculations. The first method is the equivalent earthquake load method. In this method, certain horizontal static loads are given to the masses of the building depending on their height and period. Since these loads are directional loads, the internal force diagrams in the structure appear in a specific way as we are used to. The second method is the mod merge method. In this method, vibration modes and mode shapes are found according to the structure by using the masses and rigidities of the structure. The internal forces formed by these mode shapes are found by statistical combination with one of the SRSS or CQC methods. The result of this process gives the highest internal force that the element can get at one point.
. For example, let's consider the SRSS join. In a 2-modal analysis, internal forces 4, -3 are found for each mode. Let + be tension - pressure. The value we need to use in the earthquake calculation should be the square root of the sum of the squares of these two values. that is, the square root( (4)*(4) + (-3)*(-3) ) = 5. In this case, we have an undirected quantity. Since this value is taken as - and + in combinations, the element is designed as both -5 pressure and +5 tension effect. If we had done it with an equivalent earthquake load, it would have been +5 in one direction of the earthquake (for example +Ex) and -5 in the other direction of the earthquake (-Ex). However, the mod can only see the value resulting from the merge, not the ones with + - signs in the merge results. The results will look like this in all software that performs mode fusion (response spectrum) analysis. Best regards...
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