Shear Capacity Of Prestressed Concrete Beams And Improved Truss-arch Model

Although extensive studies have been carried out on shear capacity of prestressed reinforced concrete members, there is still lack of well-accepted reasonable shear design theories for prestressed members, due to the complexcity of shear mechanisim of prestressed reinforced concrete members. At present, most design codes over the world adopt emperied equoations, leading to great varitions of calculating results. Therefore, it is necessary to investgate shear design method and theory for prestressed reinforced concrete members.The major studies carried out in this thesis were:(1) Shear design methods and theory for prestressed reinforced concrete members were summarized and factors influencing shear capacity of prestressed concrete beams were analyzed. Based on this, design equations for prestressed reinforced concrete members in different code provisions were compared.(2) A shear database for prestressed concrete beams was established and several factors such as concrete strength, shear to span ratio, effective depth, pretress ratio, longitudinal reinforcement ratio and stirrups are analyzed after dividing the database into two types:beams with stirrups and without stirrups. Effects of different factors are explored based on calculation results according to GB50010-2010and ACI318-05and several appropriate proposals are suggested with the view of improving GB50010-2010. A new formulation is introduced whose feasibility is authenticated.(3) An improved truss-arch model is proposed and a new formulation is derived. Several parameters like concrete softening coefficient, angle of inclination of struts and arch rib, prestressing steel are deliberated. New formulation is conservative and consistent after comparing and contrasting with Chinese code and American code. It is confirmed new formulation could be applied to predict shear strength of prestressed concrete beams. Following results could be obtained through this paper:1.For members with stirrups, if stirrups strength characteristic value fyvρsv>5, calcula-tion results of GB50010-2010will be overestimated.2.For members with stirrups, influence of longitudinal reinforcement ratio should be taken into account to calculate shear strength.3.Several proposals which are confirmed feasible are suggested based on calculation results of database, coefficient variation(CV) and dispersion of new formulation decrease.4.Improved truss-arch model could predict shear strength of prestressed concrete beams well, calculation results are conservative, by contrast with Chinese design code and American code, improved formulation has smaller dispersion and better applicability.