THE CONTACT SEAM WORK ANALYSIS BETWEEN CONCRETES OF DIFFERENT CLASSES IN BENT REINFORCED CONCRETE ELEMENTS

Abstract

The development of the building structure nomenclature involves the search for new types of elements made of one material or in combination of several materials for their joint mutually beneficial operation, reduction of their cost while ensuring the same load-bearing capacity, increase of  manufacturability, etc. One of the methods to restore the performance of reinforced concrete bent elements is strengthening their compressed zone. That is why the replacement of stretched concrete in such structures with cheaper material, such as concrete of a lower strength class or with porous fillers, is an urgent issue. Solving the issue of joint operation of the layers of concrete structures has a decisive impact on their overall bearing capacity. Theoretically, the operation of the contact seam can be analyzed to the fullest extent possible using the design dependencies set out in existing regulatory documents. Experimental tests were carried out on five types of concrete beams with different concrete height ratios of different classes. The beams had a rectangular cross-section with dimensions b×h=100×150 mm. The length of the beams was 1200 mm. The upper compressed part of the beams was made of C20/25 concrete, and the lower tensile part was made of C12/15 concrete. The beam was reinforced with two Ø12 mm reinforcing bars of A400C class periodical profile in the tensile zone. The beams were tested in a single-span hinged-supported scheme with a clean bend in the middle of the span. The experimental results showed that beams with a height ratio of h_C20/25/h_C12/15=3 have the largest margin of safety.