Papers by Keyword: Prestress

Abstract: The paper deals with the design and development of a new and progressive structural types of footbridges with an external tendon used as a main load bearing member. Main goals of the paper are checking the possibilities of using such structures for many different spatial arrangements and especially identifying the problematic aspects of the design. Using the results of research conducted in previous years, the procedure for finding the optimal shape of the cable was described in detail. For specific examples the process of cable shape optimizations is shown. In the next part the influence of various boundary conditions is discussed. The structures were also checked in terms of ULS and SLS limit states. Particular attention is paid to the buckling analysis of the struts and stress distribution in the deck part. The structures were modeled using FEM software Midas Civil. The models used for basic analysis consist of beam and truss elements. For precise analysis the shell models were used. Finally the dynamic behavior analysis was performed according to SÉTRA methodology. The results and outputs of the research should be used by designers who have to deal with similar structural types and they shall hopefully help to identify the most problematic features.

Abstract: This paper reports the findings from an analytical study into the influence of fiber reinforced polymer (FRP)-to-concrete interface gap and prestressed FRP tubes on strain reduction factor (k_ε) for concrete-filled FRP tube (CFFT) columns. A database that consists of a total of 45 aramid FRP- (AFRP) confined normal-and high-strength concrete (NSC and HSC) specimens with circular cross-sections is presented. All specimens were cylinders with a 152 mm diameter and 305 mm height, and their unconfined concrete strengths ranged from approximately 45 to 110 MPa. Analyses of the experimental databases that consisted of 22 specimens manufactured with FRP-to-concrete interface gap and a further 23 specimens prepared with lateral prestress is presented and discussed. Based on close examination of the hoop strain development on the FRP confining shell, expressions to predict strain reduction factors (k_ε) are proposed. The comparison of the proposed model predictions with the experimental test results of specimens prepared with an interface gap or prestressed FRP tubes shows good agreement.

Abstract: In order to meet demanding of non-magnetic, changing the reinforcement ratio, the degree of prestress and cross section form, four partially prestressed concrete beam (3 T shape section, 1 rectangle section) were made with CFRP as longitudinal reinforcement and stirrup. The results show that: the pure bending sections of the test beams conform the plane-section assumption; the beams with bigger rate of reinforcement or with stronger prestress tends to appear more cracks with smaller spacing and width, also their cracking load were higher with relatively lesser deflection. The cracking load and ultimate load of T-shape beam are slightly larger than the rectangular beam’s, but their deflections are similar nearly. Based on experimental research, nonlinear finite element analysis software ANSYS was utilized to establish the model, the results of numerical simulation and experiments showed good agreement.

Abstract: Concrete-filled FRP tube (CFFT) columns have recently gained significant research attention, with a number of experimental studies identifying significant benefits of using high-strength concrete (HSC) to produce high-performance CFFT columns. A recent experimental investigation revealed that prestressing the fibers in the fiber reinforced polymer (FRP) confining shell leads to significant improvements in the axial compressive behavior of HSC-CFFTs. This paper reports the findings from an analytical investigation into the lateral strain-to-axial strain relationship for prestressed HSC-CFFTs. This understanding of the lateral strain-to-axial strain relationship is of particular importance for prestressed CFFTs due to the influence of the additional lateral prestrain. Initially a database that consists of 23 aramid FRP- (AFRP) confined HSC cylindrical specimens with lateral prestress of up to 7.3 MPa is presented. Based on close examination of the experimentally recorded data, an expression to predict the lateral strain-to-axial strain relationship for prestressed HSC-CFFTs is proposed. The comparison of the proposed model predictions with the experimental test results for specimens prepared with prestressed FRP tubes shows good agreement.

Abstract: The compressive strength and ductility of concrete can be considerably improved by lateral confinement. In this study, an emergency seismic retrofit technique using lashing belt prestressing is used as to manually retrofit damaged reinforced concrete (RC) columns. The initial prestressing is an important aspect of this technique and is introduced by the ratchet buckle. Thus, this technique offers active and passive confinement as well as shear strengthening. Furthermore, diagonal cracks in the damaged RC columns can be closed by using the active confinement of lashing belts, and the lateral and vertical load-carrying capacity and ductility of the damaged RC columns are recovered. In this study, the recovered axial compression capacity of the retrofitted RC columns and repaired RC columns using epoxy resin was investigated. Finally, the hysteretic behavior of the shear-damaged RC columns after the proposed emergency retrofit was investigated.

Abstract: We are going to present in this article an actual problem in the production of prestressed concrete prefabricated elements. There is a problem of high transport costs in the case of bridges, that are made from prefabricates. In the production of T type or double T type cross section we can have a situation that the form could be more than 100 m long and prestressing force is self-fixed. Putting the polystyrene in the form we can produce 10 or more beams in one step. From a viewpoint of theoretical background this steel form represents a problem of stability and friction. A special steel assembled frame for the production of prestressed prefabricates could be arranged close to the bridge site. Horizontal deformations represent a special problem. Friction effect is introduced as the simplification of elastic support. Non-linear solution has been used.

Abstract: Basalt Fibre Reinforced Polymer (BFRP) is a new material in civil engineering and has shown to be a promising material for infrastructure strengthening. In comparison to carbon fiber, glass fiber and other composites, it has some advantages such as high-temperature resistance and low cost. At the Structural and Composite Laboratory at Reykjavik University (SEL) several research projects involving strengthening concrete beams and columns by using FRP materials have been on-going in recent years. These tests have shown improvements in strength and durability compared to unstrengthened concrete members. The benefit of using basalt fiber or other FRP material is that they are non-corrosive, which is a good choice for reinforcing concrete structure exposed to de-icing salts, for examples in bridge decks and parking garage elements. Also for concrete exposed to marine environment, such as seawalls, water breaks and buildings or other structures located near a waterfront. Two research projects are presented in this paper; a test of prestressed concrete with internal basalt rods instead of steel and a test of columns strengthened by wrapping fibre-reinforced composite sheets around the columns to increase their strength and ductility. These experimental tests show increasing strength and ductile for both the beams and the columns.

Abstract: In case the structure is exposed to the high temperature, the lateral shear crack is the major cause exposing the steel bar to the high temperature and also the major cause of the collapse of buildings. In the study, in order to control the lateral shear crack, the presterssing using strands in a reverse direction of the lateral shear crack has applied and the fire resistance test of the PS corrugated web composite beam has been carried out, produced in a corrugated type of the steel to increase the efficiency of the prestressing. As a result of the test, the lateral shear crack introducing the PS has been reduced but it has been concluded that in case the strands are failed, the brittle failure can be taking place.

Abstract: The aim of this paper is an introduction to a very specific area of civil engineering, which is known as tensile structures (structures acting only in tension). These structures are associated with unique aspects of their design. As a result of practically zero bending stiffness, it is not possible to separate the shape and the static analysis of these structures. Shape generation is the aim of the process well known as form-finding. As a consequence of these and many other facts, it is necessary in this case to use a special way of design process, which abounds in many differences in comparison with usual design process.

Abstract: This paper presents an experimental investigation on the influence of prestress on axial compressive behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs). A total of 12 aramid FRP- (AFRP) confined high-strength concrete (HSC) specimens with circular cross-sections were tested under monotonic axial compression. All specimens were cylinders with 152 mm diameter and 305 mm height and their unconfined concrete strengths were approximately 100 to 110 MPa. The influence of FRP prestress was examined by applying 3 different levels of lateral prestress ranging from 4.29 to 7.27 MPa. In addition to the prestressed specimens, companion specimens with no applied prestress were manufactured and tested to establish reference values. Results of the experimental study indicate that the influence of prestress on compressive strength is significant, with an increase in ultimate strength observed in all prestressed specimens compared to that of non-prestressed specimens. On the other hand, the influence of prestress on axial strain was found to be minimal, with prestressed specimens displaying a slight decrease in ultimate strain, compared to their non-prestressed counterparts. The results also indicate that prestressing the AFRP shell prevents the sudden drop in strength, typically observed in FRP-confined HSC specimens, that initiates at the transition point which connects the first and second branches of the stress-strain curves.