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In this thesis, a mechanical flexural shear model for beams without shear reinforcement is derived that accountsfor the shear transfer actions from direct strut action, compression zone, crack processing zone, aggregateinterlock and dowel action. Based on the mechanical model, a simplified closed form Critical CrackWidth Model is derived. By linking the flexural shear capacity with flexural crack widths, the influence of axialforces can be accounted for consistently within this model. The comparison of the model with shear tests onRC beams, PC beams and RC beams in tension shows a very good agreement and it can be concluded thatall relevant influence parameters are considered correctly.AbsatzMoreover, the shear capacity of beams with shear reinforcement was investigated. The behavior of beamswith very little shear reinforcement can be considered similar to the behavior of beams without shear reinforcement,but with an additional stirrup contribution. For higher shear reinforcement ratios, the beams behavein agreement with an equilibrium based truss model with a variable strut inclination. To distinguish thesefailure modes in a consistent manner, a criterion based on the mechanical shear reinforcement ratio ofthe beam was derived. On this basis, shear design procedures for the design of new structures as well as forthe economic assessment of existing structures are presented. The partial safety factors for the proposedmodels are determined by probabilistic evaluations according to EN 1990. This thesis thus presents a comprehensiveprocedure for design and assessment of structures under shear loading. Judging from test evaluationsit can be expected that the presented approaches will be especially beneficiary for the assessment ofexisting structures like bridges.
"TRB's National Cooperative Highway Research Program (NCHRP) Report 549: Simplified Shear Design of Structural Concrete Members examines development of practical equations for design of shear reinforcement in reinforced and prestressed concrete bridge girders. The report also includes recommended specifications, commentary, and examples illustrating application of the specifications. NCHRP Web-Only Document 78 contains extensive supporting information, including a database that can be used to compare the predictions from the recommended procedures to existing design procedures"--Publisher's description
For members and flat slabs without shear reinforcement, the shear and punching shear strength are often the determining design criteria. These failure modes are characterized by a fragile behaviour implying possible partial or total collapse of the structure. Despite extensive research in this field, shear and punching shear in reinforced and prestressed concrete structures, remain complex phenomena so much that the current approach is often empirical or simplified. The ability of Steel Fibre Reinforced Concrete (SFRC) to reduce shear reinforcement in reinforced and prestressed concrete members and slabs,or even eliminate it, is supported by several experimental studies. However its practical application remains marginal mainly due to the lack of standard, procedures and rules adapted to its performance. The stationary processes in precast industry offer optimal possibilities for using high performance cementitious materials such as Self Compacting Concrete (SCC) and High Strength Concrete (HSC). For the author, the combination of High Performance Concrete and steel fibres is the following step in the development and the optimization of this industry. The High Performance Fibre Reinforced Concrete (HPFRC) stands between conventional SFRC and Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). The HPFRC exhibiting a good strength/cost ratio is, thus, an alternative of UHPFRC for precast elements. The principal aim of this work was to analyse the shear and punching shear behaviour of HPFRC and UHPFRC structures without transversal reinforcement and to propose recommendations and design models adapted for practitioners. Several experimental studies on structural elements, i.e. beams and slabs, were undertaken for this purpose. Firstly, an original experimental campaign was performed on pre-tensioned members in HPFRC. A total number of six shear-critical beams of a 3.6 m span each, and two full scale beams of a 12 m span each, were tested in order to evaluate the shear and flexural strength. The principal parameter between the specimens was the fibres (...).
Development of shear databases attracted a great deal of attention in the shear research community within the last decade. Although a few shear databases have already been developed by several research groups, there is no comprehensive shear database that is focused on prestressed concrete members. This thesis aims to develop a shear database for prestressed concrete members with an intensive literature review. This literature review resulted in a database that contained a total of 1,696 tests reported in North America, Japan, and Europe from 1954 to 2010. The database was used to evaluate shear design provisions available in North America, Japan, and Europe. The variations in measured versus calculated shear strength using twelve shear design equations were analyzed. The analysis results indicated that design expressions based on the Modified Compression Filed Theory (MCFT) produced the best performance to estimate the shear strength of prestressed concrete members with sufficient shear reinforcement. The MCFT-based design expressions, however, provided unconservative strength estimations for members that failed in shear but exhibited signs of horizontal shear damage and/or anchorage zone distress. The ACI 318-08 detailed method was found to be less conservative than the MCFT-based design expressions. Additionally, on the basis of a careful examination of test results included in the database, a new limit for the minimum shear reinforcement was proposed. The database was also used to investigate the shear behavior of prestressed concrete members. This investigation revealed that there was no evidence of size effect in the shear strength of prestressed concrete members with sufficient shear reinforcement. Additionally, it was found that prestress force and shear reinforcement increased the shear strength although there was an upper limit on the effectiveness of shear reinforcement.
The first part of the report is devoted to linear elements (beams, columns) and includes chapters on shear and flexure in beams, ultimate limit state design of prestressed beams, and of reinforced concrete members under combination of bending with axial load and shear, of beams subjected to torsion, and a chapter on shear design based on truss models with crack friction. The second part treats two-dimensional elements and includes background information on ULS design of wall, shell, and slab elements. lt concludes with a chapter on axisymmetric punching of slabs.