Design of the Frame
One of the main goals pursued in the design of the new frame was that each beam could be loaded individually. Unlike other test setups previously proposed [6, 7] in which a column for three beams was designed, the solution here presented required more space since the beams were not piled but placed one next to another. Some initial estimations displayed a strength of the concrete at the mid-span high enough to think about using a system of levers to transmit and easily handle the loads. Moreover, the creep was evaluated by means of the deflection instead of measuring the crack opening or both parameters [5, 8].
The steel frame (Fig. 1) was designed to measure the creep of 12 beams at the same time. The frame consists of a system based on a three-point configuration with a distance between supports of 1100 mm (Fig. 2b). A hollow steel cylinder was placed at the centre of the upper face of each beam together with a steel sheet. Fixed to the frame, an aluminium structure above the levers and the beams is used to hold the LVDTs to measure the deflection of the beams. These LVDTs are in direct
Fig. 1 Schematic representation of the frame for the creep test
Fig. 2 a Steel frame, b three-point configuration 1100 mm length, c hollow cylinder with LVDT transducer, d hinge mechanism and e load on lever
contact with the steel sheets in the centre of the beams (Fig. 2c) and connected to a data acquisition system.
At the vertical columns, hollow steel bars of 22 mm of diameter were installed crosswise to produce the effect of a hinge mechanism to the levers as depicted in Fig. 2d. The levers were fixed to these bars at one edge and were free at the opposite edge, allowing the rotation around the longitudinal axis of the steel bar. To transmit the load to the beams, the levers rest on the steel cylinders fixed to the beams while the loads are placed on the free edge of the steel beam as shown in Fig. 2e.