Environmental Studies and Researches Institute, University of Sadat City, Egypt

Abstract

Reinforced concrete deep beams may exist in many structural applications such as offshore structures,transfer girders, pile caps, tall buildings and water tanks. The depth of deep beams is much greaterthan normal in relation to their span. Since the beam is short in this case, shear deformations are moreimportant and special design methods should be applied in this case rather than normal beam theory.Continuous deep beams are defined in the Egyptian Code of Practice (2012) [2]as those beams whoseheight to effective span ratio greater than 0.4. Deep beams are members with special features. In suchbeams, plane sections do not remain plane after bending, with significant warping of the crosssectionsbecause of high shear stresses. The resulting strain distribution is no longer linear andflexural stresses are not linearly distributed even in the elastic range. Recently, high strengthconcrete, defined by the American Concrete Institute ACI318-08[3], as concrete with cylindercompressive strength greater than 60Mpa, is being widely used in the construction industry.However, limited research efforts were directed towards the study of the behavior and shear strengthof reinforced high strength concrete continuous deep beams. Furthermore, sometimes web openingshave to be provided in deep beams for the purpose of access or for providing services. The presenceof such openings may affect the shear strength of deep beams. However, limited investigations weredirected towards the study of continuous deep beams with openings. Also, strengthening simplysupported deep beams using carbon fiber reinforced polymers (CFRP) was investigated by manyresearchers. However, limited research papers were directed towards CFRP strengthening ofcontinuous deep beams. Experimental tests have been carried out on rectangular reinforced concretecontinuous deep beams with a/d=1.17, under static loading up to failure. The study takes intoconsideration the following parameters: Percentage of web reinforcement (ρh), Positions ofopenings and number of openings. Also, strengthening of openings in continuous deep beams usingglass fiber reinforced polymer (GFRP) was studied in this research. Test results indicated that thepresence of web openings within exterior or interior shear spans had great effect on the beamcapacity and its behavior. Existence of web openings within exterior or interior shear spans caused ahigh reduction in the shear capacity of the beams by about 35%. Therefore and whenever should be kept clear of the natural load path joining the loading and reaction points (solid) free from openings.Also, the strengthening of openings contains the cracks and increase the crack and ultimate load.Finally we will compare the test results with the theoretical values for beam A1 which were evaluatedusing strut and tie analysis according to Egyptian code (2012). The strut–and tie method can be used forthe design of Disturbed regions (D- regions) of structures where the basic assumption of flexure theorynamely plane sections remaining discontinuities arising from concentrated forces or reactions and neargeometric discontinuities such as abrupt changes in cross section etc. The strut – and- tie method ofdesign is based on the assumption that the D-regions in concrete structures can be analyzed and designusing hypothetical pin-jointed trusses consisting of struts and ties interconnected at nodes. The usualdesign practice for continuous deep beams has been to employ empirical equations which are invariablybased on simple span deep beams testes. Given the unique behavior pattern of continuous deep beams,this practice is unreliable. Since continuous deep beams contain significant extents of D-regions and theyexhibit a marked truss or tied arch actions, the strut- and – tie method offers a rational basis for theanalysis and design of such beams. The mechanics and behavior of continuous deep beams are brieflydiscussed from which a strut–and–tie model for such a beam is developed.