Moment capacity in ultimate limit state is most easily calculated with a fixed neutral axis inclination, i.e. parallel to either y or z-axis. As non-linear material and cracking are assumed, iteration is required to establish equilibrium together with external normal force and at the same time calculate current moment capacity.

Start the calculation by setting maximum allowed strain in extreme concrete fiber (εc,max) and extreme reinforcement bar (εs,max) and calculate force resultants in compression zone and tension zone in order to determine if compression or tension is decisive. Iteration continues with adjustment of neutral axis position to get maximum utilization of decisive materials at established equilibrium conditions. Moment capacity may also be calculated in an optional direction, either as a fixed neutral axis inclination (other than y or z-axis) or as a fixed moment vector inclination. Iteration is generally required in the latter case to establish the neutral axis direction corresponding to the given moment vector inclination.

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PRE-Stress Documentation