For reinforced concrete and post-tensioned concrete beams and slabs, deflection control at serviceability conditions is a critical check for code compliance and satisfactory design. The ability to check if a member is cracked and has exceeded the cracking moment or threshold modulus at short- and long-term stages is a critical part of the design process.
ADAPT-Builder now gives users more control over the rupture modulus that is used when determining a member’s cracking moment. The option for the user to override the program default and user define the modulus of rupture for cracked deflection of reinforced concrete and post-tensioned slabs and beams is now included in the Criteria > Concrete input dialogue. The definition of a concrete material includes a new section for modulus of rupture.
The user-defined value for fr is used in two areas of the program:
When calculating the cracking moment, Mcr for calculation of Ieff when cracked deflection calculations are considered in the software.
In ACI 318, strength reinforcement for bonded prestressed systems should exceed 1.2Mcr. If this option is selected from Criteria > Analysis/Design Options the program calculates the cracking moments, Mcr based on the defined modulus of rupture assigned to the concrete in question. In the case where a design section intersects multiple regions with different concrete assignments, the program uses the properties associated with the concrete material having the lowest value for compressive strength, f’c.
The program does not adjust the user-defined input for concrete weight and the user-defined value should reflect any modifiers necessary to be applied to the rupture modulus.
For more information on this topic, review the video below: