Shear enhancement in RC beams with multiple point loads

• Twelve beams tested to investigate shear enhancement with multiple point loads.
• Shear enhancement method of EC2 shown to give over conservative strength predictions.
• Measurements presented of critical shear crack kinematics.
• Strut and tie modelling (STM) gives good strength predictions of tested beams.
• Best STM predictions obtained using Modified Compression Field Theory.

Eurocode 2 (EC2) allows short shear spans in reinforced concrete beams with loads near supports to be designed using either its shear provisions or strut and tie models (STM). In the case of beams with loads applied on their upper side within a distance av ⩽ 2d from the edge of supports, EC2 allows the contribution of these loads to the design shear force to be reduced by the multiple β = av/2d ⩾ 0.25 (where d is the beam effective depth). Conversely, the previous UK code BS8110 increases the shear resistance provided by the concrete within 2d of supports to vc/β (in which vc   is the concrete shear resistance in MPa) up to a maximum shear resistance of 0.8fcu or 5 MPa. The two methods are only equivalent for beams without shear reinforcement and single point loads within 2d of supports. However, there is a lack of test data to assess the comparative merits of the two methods and STM for beams with multiple point loads within 2d of supports. Therefore, twelve beams were tested with up to two point loads within 2d of supports. Significantly, BS8110 is found to give better estimates of shear resistance than the EC2 shear provisions. STM gives good predictions of shear resistance if strut strengths are calculated in accordance with the recommendations of the modified compression field theory (MCFT) but some unsafe predictions are obtained when using EC2 strut strengths.