The main reason why spiral stirrups can improve the bearing capacity of the normal section of axial compressed columns is that ( ). A: the strength of spiral stirrups is high B: spiral stirrups can effectively restrain the longitudinal reinforcements and improve the compressive strength of longitudinal reinforcements C: spiral stirrups can effectively restrain the core concrete and improve its compressive strength D: spiral stirrups have strong deformation capacity

The most effective measure to avoid the inclined compression failure for a beam is by ( ). A: increasing the amount of stirrups B: increasing the section size C: increasing the amount of web reinforcements D: increasing the amount of bent-up reinforcements