explored (Ramirez and Breen, 1991; Vecchio and Collins, 1986; Hsu, 1988). Reducing this angle implies a higher efficiency of the transverse reinforcement (as geometrically, more stirrups will cross a shear crack with a lower angle) and thus results in less shear reinforcement required for the same shear demand. The concreteshear strength contribution can be considered as well, and in early formulations, it was based on a limiting shear stress. Later it was taken to be the diagonal cracking strength (i.e. the concrete contribution at ultimate, based on test data). Code provisions such as those of ACI 318 and the AASHTO Standard Specifications take into account the effect of flexure, axial force, and prestressing into the diagonal cracking strength. However, they also make the assumption that the concreteshear strength contribution is independent of shear reinforcement. In contrast, some European design methods take θ as the angle defined by a plasticity-based model and different equations can result in values as low as 21.8 degrees. However, the concreteshear strength contribution depends on the shear reinforcement and is calculated by different expressions used that are based on shear-friction models. In AASHTO LRFD, the angle θ is often taken between 20 and 25 degrees, consequently providing a larger shear strength contribution from the shear reinforcement than that found from a 45 degree model. The concreteshear strength contribution is defined as the ability of the cracked concrete to carry diagonal tension in the web of the member, and it depends on the longitudinal strain, the reserve capacity of the longitudinal reinforcement at a crack location, and the shear-slip resistance of concrete. The Tureyen and Frosch (2003) model takes the angle θ as 45 degrees and bases the concrete strength contribution on the limiting capacity of the uncracked section (Kuchma and Hawkins 2008).
to enhance the strength, ductility, and serviceability of the structural members, utilizing the prestressing force introduced to the concrete. Although many other steel– concrete composite girder systems have been devel- oped, as shown in Fig. 1, increasing demand continues for new horizontal composite members that can ensure reliable load-carrying performances and price competi- tiveness in the current construction market (Heo et al. 2007; Kim et al. 2011; Kim and Lee 2011). Therefore, in this study, the prestressed hybrid wide flange (PHWF) girder that can effectively resist external forces was devel- oped. Figure 2 shows the main concepts and the actual construction sequences of the proposed PHWF girder. The PHWF girder system was devised and designed to achieve superior deflection control performance and high flexural and shear capacities by introducing pre- stress into the concrete bottom flange. In addition, by utilizing the embedded steel member with trapezoidal- shaped multiple openings (Fig. 2), the horizontal shear strength and the composite performance between the cast-in-place (CIP) concrete and the PHWF girder can be significantly enhanced. In addition, the top steel flange of the embedded steel member was designed to achieve the sufficient capacity under positive flexural moments
The Newmark Structural Engineering Laboratory (NSEL) of the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign has a long history of excellence in research and education that has contributed greatly to the state-of-the-art in civil engineering. Completed in 1967 and extended in 1971, the structural testing area of the laboratory has a versatile strong-floor/wall and a three-story clear height that can be used to carry out a wide range of tests of building materials, models, and structural systems. The laboratory is named for Dr. Nathan M. Newmark, an internationally known educator and engineer, who was the Head of the Department of Civil Engineering at the University of Illinois [1956-73] and the Chair of the Digital Computing Laboratory [1947-57]. He developed simple, yet powerful and widely used, methods for analyzing complex structures and assemblages subjected to a variety of static, dynamic, blast, and earthquake loadings. Dr. Newmark received numerous honors and awards for his achievements, including the prestigious National Medal of Science awarded in 1968 by President Lyndon B. Johnson. He was also one of the founding members of the National Academy of Engineering.
The available reliability methods are presented in several books [17, 18]. Reliability analysis can be performed using iterative procedures, by Monte Carlo Simulations or using special sampling techniques. Limit States are the boundaries between safety and failure. There are three types of limit states. Ultimate Limit States (ULS) are mostly related to the bending capacity, shearcapacity and stability. Serviceability Limit States (SLS) are related to gradual deterioration users comfort or maintenance costs. The third type of limit state is fatigue. This paper is focused on the ultimate limit state of the moment carrying capacity .
The materials used for this experimental work are cement, sand, water, steel fibres. Cement: Ordinary Portland cement of 43 grade was used in this experimentation. Coarse aggregate of 10-20 mm size having specific gravity of 2.70, Water: Potable water was used for the experimentation, Steel Fibers: - In this experimentation Dramix Steel fibres were used.. we casted total 18 beams, in that proportion i.e. 1% by volume of concrete and beams of same proportion, 3 for 28 days without steel fiber and also 3 plain beams for 28 days . Also by using same percentages 6 cubes are casted in that 3 are plain and 3 are with steel fiber(table 1)
Table 3-5 shows details of the six one-way walls with typical vertical GFRP grid, tested to examine the strength of the rigid foam and GFRP grid connector shear mechanism in flexure. The specimens presented in this table are defined in this report as “one-way wall specimens”, and are shown schematically in Figure 3-8 and Figure 3-9. All wall specimens were 0.6m in width, had a 3.66m span, 0.3m grid spacing, 50mm insulation thickness, and two 64mm (2.5in) concrete outer wythes. Five of the six wall specimens were flexurally strengthened after determining that the specimens were not reinforced sufficiently enough to make meaningful conclusions as to the level of composite action achieved at higher loading conditions. The strengthening was done using a Tyfo SCH 41 unidirectional carbon fiber fabric with fibers oriented in the 0º direction in conjunction with Tyfo S epoxy for wet-layup applications, having a tensile modulus of 96 GPa, maximum rupture stress of 986 MPa, and an ultimate tensile strain of 0.01 (Rutledge, 2012).
geometry, number of spans and variability of span within a bridge. Open top girders are cost effective only where standard internal forms of modular length can be utilised. The inner forms are expensive to construct and difficult to adjust for incremental length changes. Irrespective of the degree of deck skew, inner void profiles must always be detailed as square ended and internal diaphragms must be normal to the girder axis as shown in Figure 1.
Discrepancies exist between UK design codes for the prediction of pile cap shear strength. A series of reduced scale pile cap experiments to investigate shear strength have been performed. Results from seven samples are presented. Details of test methodology and procedure are shown. Final crack distributions show that pile caps under wall load behave close to simply supported two- dimensional deep beams, except for hogging cracks over the pile head indicating the existence of moment restraint at the piles. Results for failure load indicate that pile cap shear strength is at least two to three times higher than current code predictions from semi-empirical formulae. The truss method is shown to be more reliable to predict pile cap shear strength than bending theory. Keywords: pile cap; shear; truss method; shear enhancement factor.
Bentz, Vecchio & Collins (2006) observe that the shear behaviour of reinforced concrete continues to be studied, and discussed as there is no agreed basis for a rational theory, and experiments cannot be conducted for concrete beams subjected to pure shear. Shear failures of PSC beam structures are potentially brittle and could occur without warning due to the low level of shear reinforcement which is often associated with these types of beams. This brittle and explosive nature of failure was evident in the testing of PSC beams within this study. This illustrates the increased importance of being able to accurately and safely predict the shear capacities and ductility of bridge beams.
concrete bridges will be maximum compare to the other type of bridges in universal. Because construction of pre-stressed concrete bridge will be quicker, more economical sections, better quality control, suitable for repetitive construction, etc. considered model will be analyses by the code IRC (Indian road congress).finding the failure of structure applying different load combination like moving load (IRC CLASS AA), vehicle 1 combination (IRC CLASS A) and vehicle 2 combination (IRC CLASS 70R).the probability of failure will be find out by reliability analysis method. Reliability values are within assumed percentage of failure of structure hence considered bridge will be safe.
Most of the bridges on the road and motorway network were constructed in the 1960s and 1970s, and some bridges on the road network are very much older. Most were built in reinforced or pre-stressed concrete and have steel embedded within them. A combination of natural weathering, chemical attack, low quality construction materials, can cause structural deterioration. Over the years, traffic flows and the maximum permitted weight of heavy goods vehicles have both increased, and required standards of safety have improved. A combination of these factors and the deterioration of elements of a bridge create the need for strengthening.
Possible failure modes of a prestressedconcrete containment structures (PCCS) under the action of internal pressure are hoop tension; bending plus membrane stress at extreme fiber at wall-raft junction; shear near the edge and fixture on basement; and punching shear near large penetrations like airlocks. Amongst these, hoop tension at principally membrane region is reported to be the predominant one. The paper assesses the reliability of PCCS against hoop tension failure adopting first order second moment method of level-2 reliability analysis. The performance function, g (.), was formulated on the basis of standard design format of prestressedconcrete containment structure for hoop tension induced by internal pressure. Three basic variables considered are internal pressure, ultimate strength of prestressing tendons and compressive strength of concrete. Short-term as well as time dependent long-term prestressing losses are taken into account in formulating g (.). Both epistemic and aleatory uncertainties associated with basic variables are considered. It is observed from the analysis results that reliability of a prestressedconcrete containment structure deteriorates with age. It is also noted that uncertainties associated with ultimate strength of prestressing cable have maximum effect on failure probability where as that due to internal pressure and compressive strength of concrete have moderate and negligible effects respectively. Rational estimation of prestressing loss is very important for safety of the containment structure over the entire operating life.
Precast concrete parking structures allow for volume changes from creep, shrinkage and tem- perature differences. Components are cured before they are delivered to the site. The connections between members allow the structure to relieve pressures from ordinary expansion and contraction that otherwise could cause cracking in structural elements. Lateral design loads for wind, earthquake or earth can be resisted in a precast concrete structure by transferring loads through the floor diaphragm to shear walls and/or to column beam frames. Care in locating and the isolation of shear walls and isolation (expansion) joints will assure perfor- mance.
The comparison of various building code provisions for shearcapacity of low-rise reinforced concretestructural walls, including ACI 318-14, ASCE 43-05, and Eurocode 8 EN 1998-1:2004, was carried out. The structural wall has the rectangular cross section of 25×300cm and is subjected to a concentrated force at the top of the wall. Horizontal and vertical web reinforcement are the same, consisting of two layers of 14mm-diameter bars at spacing of 200mm with the design yield strength of 280MPa. From the study, the following conclusions can be drawn.
loaded till failure. It was found that the compressive strength of concrete decreased as the fire exposure time increased. It was also found that increasing the concrete cover helped to decrease the fire damage on the shearcapacity of the beams. Saafi (2002) proposed a design method to predict the residual flexural and shear capacities of FRP reinforced concrete beams exposed to fire. The method involved determining the distribution of the elevated temperatures within a cross-section and then using the degraded strength properties of FRP and concrete due to elevated temperatures. It was found that the FRP temperatures decrease with increasing the concrete cover, and FRP reinforced concrete beams exhibited significant degradation in their strength during exposure to fire. Shang et al. (2009), as reported by Xiang (2012), carried out experimental research to investigate the effect of fire on the shear resistance of eight simple beams strengthened with U-type high performance ferrocement laminate layers. Liu et al. (2009) proposed an analytical tool to predict the flexural and shear capacities of RC beams strengthened by a carbon fiber sheet exposed to fire and validated the method by test results found in the literature.
It is evident from Eqs. (43c) and (50b), that in prestressedconcrete inclined roof girders with straight tendons, the effective fictitious modulus of elasticity varies from section to section along the length of the girder. This fact necessitates evaluation of a single mean value of the effective fictitious modulus of elasticity for the entire inclined girder. Such evaluation by means of integration, however, is difficult and tedious. An approximate mean value for the effective fictitious modulus of elasticity in inclined girders could be achieved by substituting the stiffness coefficient of the mid-section between the support and the crown (midspan) in Eq. (50b).
slender and deep beams, respectively. The proportion of ALWC and SLWC beam specimens (6.9%) is very small compared with that of NWC beam specimens, indicating that further experimental investigations may be required to reasonably evaluate the shear transfer capacity of lightweight concrete in beams. Test results originally collected by Collins et al. 10 , Yang and Ashour 11 and Yang et al. 12 were the main sources of NWC beams in the database. On the other hand, test results obtained from Ivey and Buth 8 , Clarke 13 , Hanson 14 , Kim and Park 15 , Kim et al. 16 , Park et al. 17 , Thorenfeldt and Stemland 18 , and Yang et al. 5, 6 were the main sources for lightweight concrete beams. All test specimens in the database were reported to have failed in shear. The distributions of main parameters are summarized in Table 1 for deep and slender beams of different concrete types. The dry density of concrete varies between 1236 kg/m 3 (76.6 lb/ft 3 ) and 1735 kg/m 3 (107.6 lb/ft 3 ) for ALWC, and between 1700 kg/m 3 (105.4 lb/ft 3 ) and 2024 kg/m 3 (125.5 lb/ft 3 ) for SLWC. The NWC beam specimens had a relatively low f c ' of 6 MPa (0.87 ksi) and very high f c ' of 130 MPa (18.85 ksi). On the other hand, the compressive strength of LWC beam specimens ranged from 20 MPa (2.90 ksi) to 40 MPa (5.80 ksi). The longitudinal tensile reinforcement ratio varied between 0.005 and 0.035 for NWC beams, and between 0.01 and 0.03 for LWC beams. Deep beams are primarily tested at a / h between 1.0 and 2.0, whereas a / h of slender beams mostly ranged between 2.5 and 5.0 for NWC and between 2.5 and 3.0 for LWC. All of the collected deep beams were reported to be failed owing to crushing and sliding of concrete struts joining load and reaction points.
large cracks and spalling of concrete exposing prestressing strands. The CFRP repair system was designed using a simple section analysis procedure to ensure that the new flexural strength was equal to or greater than that of the original girder. Detailing of the CFRP repair system followed industry standards and provided transverse U-wraps at 15.75 in (400 mm) spacing and extension of the CFRP well away from the damaged concrete area. Experimental testing was limited to bond and adhesion tests to ensure proper bond of the CFRP to the concrete substrate. In the second project, a prestressedconcrete bridge girder was repaired in-situ with CFRP wet lay-up sheets after impact damage ruptured two prestressing strands (Tumialan et al. 2001). The design of the repair system was determined by the rectangular stress block approach. Two layers of CFRP sheets were applied to the tension face, extending past the damaged location. CFRP U-wraps were also applied to prevent debonding failure. Following current industry standards, the CFRP repair system was successfully installed by a contractor. Field testing was not performed, however the repaired girder is performing well in service.
The containment of the French 1300/1450 MWe pressurized water reactors is ensured by two concrete vessels. The inner containment is biaxially prestressed so that it remains in compression under the pressure and temperature loading associated with a LOCA. It’s design is based on hypotheses concerning creep and shrinkage induced loss of prestress. These phenomena must be accurately monitored and their evolution must be accurately predicted in order to estimate the capability of the structure to undergo accidental conditions in the future during its whole industrial lifetime. The prediction of the further delayed behaviour of the containment vessel must be able to account for the previously monitored behaviour, the uncertainties associated to the measurements and the uncertainties associated to the model parameters.