End Anchorage Research Articles

An experimental study of the anchorage length of carbon fibre composite plates used to strengthen reinforced concrete beams

Concrete structures deteriorate for various reasons and upgrading has been achieved for over 20 years by bonding steel plates using epoxy resins. Disadvantages of this method include transporting, handling and installing heavy plates and corrosion of the plates. The use of composite materials overcomes these problems and provides equally satisfactory solutions. The rehabilitation of concrete structures represents a large demand for efficient strengthening methods and composite materials are well suited to this application. It is now necessary to understand more about the factors that are important in the design of composite plate bonding, such as the influence of the plate anchorage length and additional plate end anchorage. Four point bending and cantilever loading are used to show that the ultimate capacities and failure modes of reinforced concrete beams, externally strengthened with bonded composite plates, are dependent on the shear span/depth ratio. Strengthened members are found to fail by separation of the concrete cover from the internal rebars throughout the whole of one shear span under low shear span/depth ratios, while a thinner concrete layer is separated at higher ratios. Peeling of the plate end is thought to occur under low shear span/depth ratios. The end of the bonded plate in the failed shear span experiences strain increases relatively soon after yield of the internal steel when the shear span/depth ratio is low, but the plate ends are less sensitive to yield under higher ratios, indicating the lower shear transferred into the concrete via the adhesive at the plate ends. Ultimate bending moments are found to reach an upper limit with increasing shear span/depth ratio in the range of ratios studied. Adhesive shear stresses are of greatest magnitude at the ends of the plate under low shear span/depth ratios.

An experimental study of the influence of plate end anchorage of carbon fibre composite plates used to strengthen reinforced concrete beams

Carbon fibre reinforced polymer (CFRP) materials are well suited to the rehabilitation of civil engineering structures due to their corrosion resistance, high strength-to-weight ratio and high stiffness-to-weight ratio. Their application in the field of strengthening is envisaged to expand due to the vast number of bridges and buildings in need of strengthening. In order to apply these materials effectively, it is necessary to understand the behaviour of members strengthened with externally bonded composite plates, one aspect of which is the response to the installation of anchorage at the ends of the plates to resist plate separation from the beam. A number of 1.0 m long plated beams were tested in four point bending and as cantilevers to demonstrate that the structural benefit of plate end anchorage diminishes as the shear span/depth ratio of the beam increases. Under a low shear span/depth ratio (3.00 in the present work), the anchorage improves the composite action between the plate and the beam, giving rise to greater structural stiffness after yield of the internal rebars. This beneficial influence can be achieved using a bolted anchorage system which provides the same improvement in composite action as a large plate end clamping force generated by trapping the plate under the beam supports. Although the plate end anchorage has most structural benefit under a low shear span/depth ratio, it is recommended that anchorage be applied in every case until long term practical experience suggests otherwise.

Evaluation of concrete bridges by impact-echo : Ghorbanpoor, A.; Virmani, Y.P.; Fatemi, G.R. Nondestructive Testing of Concrete Elements and Structures, San Antonio, Texas (United States), 13–15 Apr. 1992, pp. 82–93. Edited by F. Ansari and S. Sture. ASCE (1992)

Strength of post-tensioned bridge structural members primarily depends on the tensile capacity of their post-tensioning steel reinforcement. To prevent corrosion, the post-tensioning steel is normally encased in plastic or galvanized metal ducts filled with a grout mix. However, corrosion of the steel can result if the ducts are not filled completely. In addition, use of an improper grout mix may result in partial filling of the ducts and/or grout bleeding, which is the separation of water from the cement paste. When bleeding of the grout takes places, the bleed water is usually absorbed back into the hardened grout and a bleed void, sometimes as long as the entire length of the duct, is left in the duct. The bleed voids could be a major factor in the corrosion of post-tensioning steel by facilitating penetration and movement of salt water and other harmful solutions inside of the ducts from the end anchorage areas or cracks, or other flaws, in the surrounding concrete. This study has examined the application of and further development of a non-destructive evaluation technique, the Impact-Echo, for determination of location and extent of voids in the ducts of post-tensioned bridge structural members. Theoretical, laboratory, and field studies have been performed and it has been demonstrated that it is possible to detect, with high reliability, the location and extent of voids in the post-tensioning ducts of concrete structures. It was found that information corresponding to the location of voids within concrete members may readily be obtained by examining the wave reflection frequency values, from an induced impact at the surface of the member, due to the incidents at the free boundaries of these voids.

A PRELIMINARY EVALUATION OF CARBON FIBRE REINFORCED POLYMER PLATES FOR STRENGTHENING REINFORCED CONCRETE MEMBERS.

Keywords SURREY UNIVERSITY CONCRETE, REINFORCED, MEMBERS, PLATES, CARBON, FIBRES, POLYMERS, STRENGTHENING, EVALUATION, REINFORCEMENT, BEAMS, BONDED, COMPOSITE, LOADS, CONFIGURATION, CAPACITY, ULTIMATE, RATIOS, SHEAR, SPANS, DEPTH, FAILURES, TESTS, DETERIORATION, STRUCTURES, UPGRADING, BRIDGES, FRP, MATERIALS, STEEL, BARS, CFRP, STRAIN, ADHESIVES, STRESS, ENDS, ANCHORAGES... Show All

Flexural Behavior of Precracked Reinforced Concrete Beams Strengthened Externally by Steel Plates

This paper presents comprehensive data and their interpretation on the plate bonding repair technique in terms of effects of plate thickness and end anchorage on ductility, ultimate load, and mode of failure. Reinforced concrete (RC) beams were preloaded to 85 percent of their ultimate capacity and subsequently repaired by bonding steel plates of different thicknesses with and without end anchorages. Anchor bolts were used for end anchorages. The repaired beams showed higher strength than the original beams, provided the plates did not exceed a certain limiting thickness. Increasing the plate thickness changed the mode of failure of the repaired beams from flexural to premature failure, developed due to shear and/or tearing of the plate, causing a reduction in ductility. End anchorages to the bonded plates could not prevent the premature failure of the beams but improved ductility with decreasing significance as the plate thickness increased, and yielded a marginal improvement in ultimate strength. A procedure for designing the bonding plate to avoid premature failure is suggested.

Partial shear connection design of composite slabs

A new partial shear connection strength model has been developed which considers the equilibrium of a segment of a simply-supported composite slab under any loading condition. The model incorporates shear connection performance derived from a new test called the slip block test. This small-scale test shows that shear connection performance is affected by factors such as profile geometry, base metal thickness and concrete compressive strength. Full-scale slab tests have proved that it is a reliable physical model which can readily account for the effects of changes in shear connection performance, loading pattern, sheeting end support conditions, end anchorage devices, conventional reinforcement etc., and is being developed for possible use in an Australian Standard on the design of composite slabs. The ease with which the model can be used in design is demonstrated in a worked example. Another new ultimate strength method of design, published by the Steel Deck Institute in America, is examined in the worked example, and shown to give erratic, sometimes overly conservative but often very unsafe predictions for the particular profiled sheet and design situations studied.

Composite Slab Behavior and Strength Analysis. Part I: Calculation Procedure

A new calculation procedure is described that provides an alternative to full-scale testing for composite slabs with ribbed decking used in buildings. The procedure consists of combining shear-bond test results with a numerical analysis to predict the behavior and strength of composite slabs. It may be used to analyze either single spans or multiple spans. The procedure incorporates certain simplifications and assumptions that allow for reasonable yet conservative prediction of both behavior and strength. In particular, chemical bonding between the concrete slab and decking and concrete tension behavior are ignored because they are brittle in nature. Advantages of using this procedure rather than full-scale test results are versatility and reduced cost, the estimation of deformations at working loads, the inclusion of additional variables such as end anchorage (over the end supports), additional positive moment reinforcement (in the span), and reinforcement in negative moment regions (near interior supports). This calculation procedure may also be used for the development of new decking and to improve the performance of slabs with existing decking. Examples of calculations are presented for single-span composite slabs.

Composite Slab Behavior and Strength Analysis. Part II: Comparisons with Test Results and Parametric Analysis

The results of selected tests on full‐scale one‐way single and continuous span composite slabs with ribbed decking are presented. Variables investigated in these tests include the number of spans, the presence of embossments in the decking, end anchorage (both welded and shot‐fired shear connectors), and negative moment reinforcement near interior supports. An example comparison is given between a standard test and the calculation procedure combining shear‐bond test results with a finite element analysis (the calculation procedure was presented in part I). The importance of composite slab internal moment resistances as a function of the applied load is examined. For a composite slab, three internal moment resistance elements are of importance: the decking, concrete slab (including additional reinforcement), and the interaction between decking and concrete slab. Parametric analyses based upon the calculation procedure predictions are performed for three decking geometries using limiting slenderness ratios. Decking types were chosen to represent a wide range of shear bond connection characteristics. Slenderness ratio is defined as the span length divided by the total composite slab depth. The effects of eleven parameters are investigated for each decking and slenderness. Effects studied include the load‐carrying capacity at service deflection limits (L/250), ultimate deflection limits (L/50), and maximum load‐carrying capacity.

Anchor Design for Slope Stabilization by Surface Loading

The increase in slope stability by application of discrete surface loads depends in part on the orientation of the load. For stabilization systems such as anchored geosynthetics, the load orientation corresponds to the angle of anchor installation. A theoretical study is performed to determine the optimum orientation of such anchors in purely cohesionless soils to maximize the increase in slope stability. Three cases are analyzed: a hypothetical surface load without anchorage, surface load with grouted end anchorage, and surface load with driven friction anchors. The last case involves the most interesting analytical solution since the optimum anchor orientation is a function of the slope geometry, the in situ stresses, and the desired increase in factor of safety. The required length and spacing of anchors depend, in addition to the aforementioned factors, on the anchor diameter, the internal friction angle of the soil, the soil-anchor interface friction, the strength of the geosynthetic, and the depth of the potential failure surface. A simplified equation is given for the anchor orientation, and a design chart is presented for determining spacing and length requirements. An example problem illustrates the importance of proper anchor orientation.

External Reinforcement of Concrete Beams Using Fiber Reinforced Plastics

A series of 16 under-reinforced beams was tested to study the effectiveness of external strengthening using fiber reinforced plastic (FRP) plates. Plates of glass, carbon and aramid fibers were bonded to the tension side of the beams using a 2-part epoxy. An interative analytical method was developed to predict the stiffness and maximum strength in bending of the plated beam. Increases in stiffness (over the working load range) from 17 to 99 percent and increases in strength (ultimate) from 40 to 97% were achieved for the beams with FRP plates. Predicted and acutal load-deflection curves showed fairly good agreement, although generally the theoretical curves were stiffer. Experimental failure did not occur in the maximum moment region on many of the beams, despite attempts at end anchorages to postpone local shear failure. The ulltimate loads of the beams that did fail in the maximum region were within about 5% of predicted values.

Longitudinal stress wave propagation in an unbonded prestressing tendon after release of load

Longitudinal stress wave propagation due to the cutting of an unbonded prestressing tendon during demolition has been studied using the finite element method. The grease layer surrounding the tendon provides a substantial viscous damping, which was represented by a linear Maxwell model with a cut-off at a limiting value of damping force. The model was validated, and damping parameters determined, by comparison with laboratory test results for tendons up to 7.4 m in length. The model was then extended to examine the behaviour of tendons longer than those tested in the laboratory. The effect of energy absorption at mortared-in end anchorages was also included. It was found that tendon displacements were small for all the lengths and tendon diameters considered.

Hysteretic restoring force characteristics of unbounded prestressed concrete framed structure under earthquake load

An analytical method, by which hysteretic restoring force characteristics of unbonded prestressed concrete framed structure can be statically pursued on the basis of material properties, is presented. The bond-slip relationship between concrete and prestressing tendon is taken into account, and thus the method covers unbonded members and bonded members. For verifying the propriety of the analytical method, the experiment is carried out on a portal frame with an unbonded prestressed concrete beam of 4.2 m in length and reinforced concrete columns of 1 m in height. High intensity reversed cyclic lateral loading is applied. The experimental results show a good agreement with the analytical ones in terms of load-deflection relation and the fluctuation of the tendon stress at anchorage end.

Shear-bond capacity of composite slabs made with profiled sheeting

An experimental study conducted to determine the shear-bond capacity of concrete slabs reinforced with locally available profiled steel decks is reported in this paper. Ten one-way slab specimens were tested under third point loading. In the light of these test data, the currently available design methods have been reviewed, and an empirical relationship is proposed to estimate the shear-bond capacity of this type of slab with and without end anchorages under third point loading.

Nonlinear contact problems—A finite element approach implemented in ADINA

In the analysis of structures or materials which consist of two or more components, special attention must be paid to their interaction. Whereas the assumption of complete compatibility between adjacent elements usually is sufficient in a global analysis, a more detailed calculation requires the realistic modeling of the contact interface. For this purpose an isoparametric contact element has been developed which is compatible to the two- and three-dimensional elements available in ADINA. The element can be used with a linear, quadratic, or cubic interpolation function. According to the isoparametric concept, curved element boundaries can be modeled respectively. At first, the element has been developed for the investigation of bond between concrete and reinforcement. Various bond stress-slip relations have been programmed including effects which significantly influence the bond behaviour, for example transversal pressure, although the application of the element is not restricted on bond problems. Due to the modular structure of ADINA, which has been maintained in the programming of the contact element, additional stress-slip relations can be incorporated on the level of the contact model. The application of the element with different contact models is shown in three different examples. The end anchorage of a reinforcement bar in a concrete block, the shear transfer across discrete cracks, and the joints of prefabricated wall structures are three examples which show the scale of application of the element.

Bond between prestressed steel and concrete—computer analysis using ADINA

A comprehensive test series was carried out to study the load carrying behaviour of pretensioned hollow-core slabs, which are not in accordance with the German building codes because of their geometry and the lack of conventional reinforcement. It was found that a number of problems concerning the end anchorage zones of the slab cannot be simply solved by experimental means with reasonable expense. Therefore a finite element analysis using the ADINA program was carried out. The intent of this contribution is to show that the modular structure of the ADINA program is extremely suitable for modification by the user for the analysis of structures whose load carrying behaviour cannot be reproduced adequately by the original version of the program. A contact element with a nonlinear bond-slip-relation is presented and added to the program, maintaining completely its modular structure. Special attention is paid to the derivation of the bond stiffness, which is of special influence on the numerical results. The validity of the computer analysis is judged by comparing test measurements of bending tests and analytical results. Although this study is restricted to a 2D representation of the real three-dimensional reinforced concrete structure with a varying cross-section (and is intended to be a preliminary study), the results are excellent and can be used to draw conclusions for the design problem.

Flexural Crack Width in Partially Prestressed Concrete Beams

Partially prestressed concrete beams, those which are designed for a limited level of tensile stress, have several advantages over their fully prestressed counterparts — there is a better control of camber, a savings in prestressing steel and end anchorages, and a more economical utilization of mild steel. Partially prestressed concrete beams do, however, have several disadvantages: 1) Reduction in the ultimate strength; 2) increased deflection under overload conditions; and 3) cracking. This note is based on a recent study of flexural cracking in partially prestressed concrete beams which include the examination of all available experimental data.

Arch Action and Bond in Concrete Shear Failures

Numerous investigators have suggested that a cracked reinforced beam without web steel behaves like a tied-arch. From a study of strain measurements in steel and on concrete, it is shown that a normally reinforced beam failing in shear behaves essentially like a beam up to failure, in spite of extensive cracking and deformation. External loads can be resisted by arch action only when the web acts in compression. Data reported show that such action can be developed in a beam only when the steel is fully unbonded between strong end anchorages. Arch action enhances the shear resistance of an unbonded beam beyond that of a bonded beam failing in shear but also increases deflection and reduced the flexural capacity. Lack of bond, however, is not a guarantee against shear failure or even diagonal cracking. The surface conditions of the longitudinal steel are shown to have limited influence on ultimate shear resistance.

End Anchorage of High Strength Steel Reinforcing Bars

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Durability of Prestressed Concrete Beams

The durability of pretensioned and posttensioned concrete beams is being studied using laboratory-prepared beam specimens. A group of beams containing pretensioned strands, some made with airentrained concrete and others with non-air-entrained concrete, was exposed to natural weathering. Sixteen beams were subjected to freezing in air and thawing in seawater at Treat Island, Maine, and three beams were exposed to sulfate attack in warm seawater on the Florida coast. In Maine the nonair-entrained concrete beams failed during the first winter; the air-entrained beams remain in good condition after five winters. No significant results have been observed at the Florida exposure. A group of posttensioned beams, all made with air-entrained concrete, was also exposed in Maine. Four posttensioning systems with either external or flush end anchorages, and 12 types of end-anchorage protection were used. The auxiliary steel reinforcement had a nominal 3/a in. concrete cover. After two winters of exposure, two of 40 end-anchorage protections have become detached, two have become loose, and several have developed a narrow crack at the bond with the beam. In all of the beams that show evidence of failure, portland cement concrete was used to enclose external anchorages. It is concluded that (1) Concrete for prestressed structural elements that are to be exposed to freezing and thawing in a moist condition should contain entrained air. (2) The concrete cover over reinforcing should be greater than '3/a in. when exposure to seawater is involved. (3) Epoxy concrete is superior to portland cement concrete for end protection. Flush anchorages appear to be more effectively protected than external anchorages.

Additional notes on the adult and larva ofsiboglinum fiordicumand on the possible mode of tube formation

Abstract S. fiordicum and S. holmei appear to be closely related. The distinction between the two is to be found in the “zone of thickened papillae” and the postannular region. As the hind end (anchor) is unknown for S. holmei the question as to whether these two species should be classified as a single species cannot at this juncture be contemplated. The bridle is considered as the tool by means of which the animal smears the exudate onto the inner surface of the tube. The larvae of S. fiordicum develop the bridle before they leave the maternal tube. The larval dorsal ciliary field divides into an anterior region which is lost in the adult, and a posterior region which is retained as the dorsal ciliary field of the metameric region.