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This paper presents an investigation on the compressive behavior of plain concrete columns confined with steel-reinforced grout (SRG) composites. The test parameters include size and cross-sectional shape (square or circular) of the columns, and number of layers (one or two) and density (low or medium density) of the steel fiber sheet. Out of 46 specimens herein presented, 33 were confined with SRG, and the remaining 13 columns were left unconfined for comparison. The results indicate that application of SRG composites improves both the average strength and the ultimate strain of confined specimens with respect to the control (unconfined) columns. The best performance in terms of strength and ultimate strain increase with respect to the control columns is obtained for small square and cylindrical columns confined with two layers of low-density fiber sheet.

RESUME Pour evaluer le module de rupture et la resistance au cisaillement du beton de masse repare par injection de coulis, six specimens de 400 x 400 x 1250 mm en beton avec des agregats de taille maximale de 100 mm ont ete testes suivant la norme ASTM C78 et avec une configuration de chargement favorisant de grandes contraintes de cisaillement le long d'un plan de rupture vertical. L'essai de la norme ASTM C78 a ete effectue sur tous les echantillons non-fissures et sur les echantillons repares (deux specimens a reparation simple et deux a reparations multiples en utilisant deux coulis d'injection microfins avec un ratio eau/ciment (e/c) de 1,0 et 0,5 respectivement. L'essai de cisaillement a ete effectue sur deux specimens a reparation simple et deux specimens a reparations multiples, injectes dans les deux cas avec les deux melanges de coulis. Une resistance a la traction indirecte moyenne de 2,8 MPa a ete obtenue pour les echantillons vierges. Cette valeur a ete diminuee a 1 MPa et 0,5 MPa pour les echantillons repares a l'aide du coulis avec rapport e/c egal a 0,5 et 1,0 respectivement, quel que soit le nombre de reparations. La resistance au cisaillement des specimens est affectee a la fois par le rapport e/c du coulis d‟injection et par de la largeur des fissures reparees.----------ABSTRACT To evaluate the modulus of rupture and the shear strength of mass concrete repaired by grout injection, six 400 x 400 x 1250 mm concrete specimens with a maximum aggregate size of 100 mm were tested following ASTM C78 and a loading configuration promoting large shear stresses along a vertical failure plane. ASTM C78 was done on the all virgin specimens and on repaired specimens (two repaired once and two repaired multiple times) using two different micro fine injection grout mixes with water cement ratio (w/c) of 1.0 and 0.5. The shear test was done on two single repaired and two multiple repaired specimens; with both grout mixes. Average indirect tensile strength of 2.8 MPa was obtained for virgin specimens. This value was reduced to 1 MPa and 0.5 MPa for specimens repaired using grout with a w/c ratio respectively equal to 0.5 and 1.0 regardless of the number of repairs. The shear strength of the specimens is affected by both the injection grouts w/c ratio and the repaired crack width.

Post-tensioning (PT) tendons in segmental bridges are often anchored within the deviator and pier segments. The effectiveness of the PT system is therefore dependent on proper anchorage function. However, anchorage failure may occur due to corrosion of the strand at the anchor head and subsequently cause the PT force to transfer within the pier segment or slacking of the tendon to occur. Following tendon stressing, the anchorage assembly and ducts that house the tendon are filled with grout. These short bonded regions could, in the event of anchorage failure, provide secondary anchorage. This paper presents the results of a full-scale experimental investigation on bonded anchorage tendon pullout. The study focuses on the embedment length required to develop the in-service PT force within the pier segment. Seven, twelve, and nineteen 15 mm (0.6 in.) diameter low-relaxation strand tendons with various bonded lengths were considered.

In the United States, segmental box-girder bridges are typically constructed with external post-tensioned (PT) tendons that are grouted for corrosion protection. The prestressing steel in these tendons often provides a significant portion of the load-carrying capacity of the bridge. Nondestructive methods, such as vibration-based techniques, have been used successfully in the field to estimate the tensile force in the tendons under service loads. Laboratory tests were conducted to understand how the tensile force and natural frequencies vary as localized damage accumulates in grouted tendons. Test results demonstrated that the service-level tensile force in the tendon decreased with increasing corrosion damage to the prestressing steel, but that significant tensile forces were transferred through the grout/duct. Redistribution of tensile forces is typically not considered when evaluating the behavior of grouted tendons, and use of standard approaches may significantly overestimate the residual tensile capacity of a damaged PT tendon.

External post-tensioned (PT) tendons in bridges are installed inside box girders with high-density polyethylene ducts. Voids in these ducts can lead to corrosion of the PT strands, which could lead to tendon failure. A grout injection is commonly used to protect exposed tendons. Although experiments using external PT tendons have been performed to investigate effective grouting repair methods and materials, these experiments cannot simulate all parameters of grouting repair encountered in the field. In response, the current study uses a commercial computational fluid dynamics program to investigate grout flows in void-containing ducts. A simplified numerical model then is developed based on previous experimental results. This model can consider all parameters of repair grouting methods not covered by experiments. A validation of the proposed model shows close agreement between numerical and experimental results regarding grout flow and repair performance.

Jacketing can be an effective way to improve the performance of the lap-spliced region of reinforced concrete (RC) columns. This paper introduces a new steel-jacketing method for RC columns that uses external pressure to attach the steel jackets to the column surface. The advantage of this method is that it does not require the application of grout between the steel jackets and the concrete surface to attach them together. Experimental tests of twelve concrete cylinders and four RC columns are performed to assess the effectiveness of the proposed method. Both single-layered and double-layered jackets are tested. The newly jacketed cylinders show good results in terms of increasing the compressive strength and ductility compared to plain cylinders. The double-layered jackets are estimated to show equal performance to that of a single steel jacket with the same thickness. The proposed steel-jacketing method increased the ductility of lap-spliced RC columns. The double-layered jacket appeared to perform better in terms of increasing ductility and energy dissipation capacity than the single-layered jacket.

One method of connecting a column to a cap beam in bridge bents is to precast the column with projecting bars, which are then grouted into ducts in the cap beam. Bar-duct systems can be assembled rapidly if a few large bars and ducts are used to connect the column and cap beam. However, the required anchorage lengths for the large bars can exceed the length available. This study evaluates the anchorage requirements for this situation by performing 14 pullout tests on bars with sizes up to No. 18. The tests and a nonlinear finite element model showed that, under conditions similar to those tested, large bars can develop their yield strength in as few as six bar diameters and fracture strengths in as few as 10 bar diameters. In all the tests, failure occurred either by formation of a cone near the grout surface combined with shearing along the confined bar-grout interface or by bar fracture. The specimens did not fail by duct pullout or concrete splitting. Polypropylene fiber reinforcement typically lowered the peak pullout strength of the bar and had mixed impact on the post-peak response.

This study investigates the performance of different temporary corrosion protection methods for prestressing steel. Four types of laboratory corrosion tests with three emulsifiable oil products in three concentrations resulted in the selection of one product that showed by far the best corrosion protection behavior. Field tests during the winter on 16 transverse deck post-tensioning tendons of 2 road bridges demonstrate the practical suitability of the selected product. Using this product, a pullout test with a long embedment length was performed on a post-tensioned seven-strand tendon with a plastic duct and compared with a reference test using untreated strands. A bond shear stress reduction by a factor of approximately 2.5 was observed compared with the untreated strands. This reduction does not appear to significantly influence the load-deformation response of post-tensioned concrete members and suggests that the emulsifiable oil does not need to be removed before grouting of the tendons. However, since the bond reduction caused by emulsifiable oils in grouted tendons may lead to a somewhat soft load-deformation response of post-tensioned concrete members in the decompressed state, a lower-bound estimate of the corresponding stiffness can be obtained if necessary by assuming a completely unbonded behavior of the post-tensioning tendons.

Engineers have proposed relocating externally bonded strengthening fiber reinforced polymer (FRP) material from the unprotected exterior of the concrete to the protected interior. This technology is known as near-surface mounted (NSM) strengthening. In NSM reinforcement, the FRP is surrounded by concrete on three sides so the bond and damage problems associated with externally bonded FRP strengthening systems are reduced or eliminated. This paper presents experimental results from 12 full-scale concrete beams strengthened with NSM carbon FRP (CFRP) strips. Three companion unstrengthened specimens were also tested to serve as a control. Experimental variables include three different ratios of steel reinforcement and two different ratios of CFRP reinforcement. Yield and ultimate strengths, flexural failure modes, and ductility are discussed based on measured load, deflection, and strain data. Test results show measurable increases in yield and ultimate strengths in all beams strengthened with CFRP as well as predictable nominal strengths and failure modes. Force transfer between the CFRP, epoxy grout, and surrounding concrete was able to develop the full tensile strength of the CFRP strips. Energy and deflection ductilities were reduced for CFRP strengthened beams. Future research needs are addressed.

The implementation of a prefabricated full-depth precast concrete deck system is an innovative technique that accelerates the rehabilitation process of a bridge deck extending its service life for the purpose of reducing user delays, and community disruptions and lowering its life-cycle costs. A full-scale, two-span continuous prototype bridge 82 ft (25 m) long and 18 ft (5.5 m) wide was designed, constructed, and tested for service load, overload, and ultimate load to study the constructibility and structural performance of the prefabricated full-depth precast concrete bridge deck system. The bridge superstructure is composed of 11 prefabricated full-depth precast concrete panels placed on three steel beams (W18 x 86) and made fully composite with shear connector pockets and shear studs. The experience gained from the sequence of construction events such as fabrication, handling and erection, grouting of transverse joints, longitudinal post-tensioning, and grouting of haunches and shear connector pockets in addition to the results derived from testing a full-scale prototype bridge indicated that a prefabricated, post-tensioned deck system is workable and constructible. Finite element analysis and experimental test results also indicated that a full composite action was maintained between the post-tensioned precast concrete panels and the supporting system; also, no cracks were observed in the transverse joints at the negative moment regions.

The application of steel-reinforced polymer (SRP) composites in structural strengthening is a new concept based on the use of high-strength steel cord. This paper presents the results of an experimental program on the flexural behavior of reinforced concrete (RC) beams strengthened with SRP, including the performance of epoxy resin versus cementitious grout to impregnate and bond SRP to concrete, as well as the feasibility of nailing the SRP to prevent peeling. The use of cementitious grout is highly relevant as it could overcome the issue of fire resistance and further reduce the cost of the strengthening system. Test results were compared to those from beams strengthened with carbon fiber-reinforced polymer (CFRP) under the same experimental program. This preliminary work shows the high potential of SRP strengthening systems and identifies some critical issues that should be investigated next in order to optimize the effectiveness of the proposed strengthening solution.

The use of anchors for attachments of structural members to concrete come in two general categories: cast-in-place and post-installed. The use of post-installed anchors allows greater flexibility in planning, design, and strengthening of concrete structures. This article reports on a study of the load-deflection behavior of adhesive and grouted anchors embedded in both plain and steel fiber-reinforced normal- and high-strength concretes. The authors tested 12 and 16 mm-diameter adhesive anchors at embedment depths ranging from 40 to 160 mm. Grouted anchors of 16 mm diameter were tested at 80, 120, and 160 mm embedment depths. A total of 57 anchors (39 adhesive and 18 grouted anchors) were tested under monotonic tension loading. Test results showed that pullout capacities of the anchors were not significantly affected by the addition of steel fibers into the concrete. Anchor tests ending with concrete failure resulted in severe damage on plain concrete. With the addition of steel fibers, however, the damage on concrete was significantly reduced. The ultimate capacity of the anchors generally increased with increasing concrete strength. The authors note that current design methods (ACI 349-85 and concrete capacity design [CCD]) overpredicted the pullout capacity as governed by concrete failure.

This paper gives test results from 4 precast concrete beam-column connections and 1 monolithic concrete connection. The tests comprised the 2nd phase of an experimental program on a 2/5-scale model precast connection. The aim of the test program was to design a simple moment-resisting precast connection for regions of high seismicity. The connection transfers bending moment by a combination of lap-splicing and end anchorage of bars. The end portions of precast beams sit on the column bearing area at the beginning of subassemblage construction. Variables examined included the level of axial load on column, spacing of beam stirrups in the connection length region, gravity load on beam, and use of steel fiber in grout of connection region. Specimens were subjected to reversed cyclic loading in accordance with a prescribed displacement history. Connection performances were compared with prior tests based on ductility, energy dissipation capacity, flexural strength, and drift capacity. The simple precast connection matches the performance of monolithic connections indicating its suitability for seismic zones.

Section 11.7 of American Concrete Institute (ACI) 318-95 contains design provisions for conditions where direct shear transfer through shear-friction should be considered. Such conditions include an interface between concretes cast at different times. Shear-friction capacity is defined by this code as a function of steel reinforcement area contained in the interface and treatment provided to the interface before the new concrete is cast against the hardened concrete. The code also considers the presence of permanent net compression across the interface and specifies an upper limit on interface shear capacity. The test results discussed in this paper are used to verify and extend the application of shear-friction provisions currently incorporated in the ACI Code. Modification and expansion of the current code are proposed in light of the additional research information available to date.

The appearance of longitudinal cracking and spalling in the web section near the end block of Florida bulb-tee concrete girders have raised some concerns regarding possible problems which may be inherent in the design and construction procedures of the girders. Several factors believed to cause the stress buildup and the cracking were investigated in this study. Results showed that stress accumulation started at the end of the transition section where the web width gradually reduced to 178 mm (7 in.). A wedging effect due to out-of-plane stresses was the most critical factor causing stress buildups in the transition zone. The effect of grout pressure was more severe in ducts with oval cross sections than in round ones.

The authors describe the effects of hole preparation method, grout type, hole diameter, bar size, embedment length, cover, bar surface condition, orientation of the installed bar, and concrete strength on the bond strength of grouted reinforcing bars. Hole preparation method, using a high-speed vacuum drill or a hand-held electric hammer drill, and cleaning methods, using a fiber bottle brush with water, a fiber bottle brush without water, or compressed air only are compared. Two capsule systems, two two-component grout systems, and two nonshrink grout systems are evaluated. Bar installations include vertical, sloped, and horizontal bars. Test results are used to develop rational design and construction requirements. The bond strength of grouted reinforcing bars is not highly sensitive to differences in the hole preparation or cleaning methods studied. Grouts that provide strong bond at the grout-concrete interface provide higher bond strengths than grouts that undergo failure at the grout-concrete interface. With the exception of bars anchored by capsule systems, the bond strength provided by grouts is not sensitive to hole diameter. Bond strength increases with increasing embedment length, cover, and bar size. The bond strength of grouted reinforcement is insensitive to the presence of epoxy coating. Vertically and horizontally anchored bars may display different bond strengths, depending on the grout used.

A nondestructive testing technique that uses transient stress waves is part of an ongoing research program at Cornell University, which is aimed at developing the theoretical basis and practical applications for the impact-echo method. This paper describes a phase of the program involving detection of voids in grouted tendon ducts in post-tensioned concrete structures. Findings from the numerical finite element studies, controlled-flaw laboratory studies, and a field study are presented. Three-dimensional dynamic finite element analyses were performed to examine the response of fully grouted, partially grouted, and ungrouted tendon ducts to transient stress waves. Laboratory specimens were constructed and tested to confirm the numerical results. Numerical and laboratory studies showed that the impact-echo method could be used successfully to detect both complete and partial voids in grouted tendon ducts. A field study was then conducted on an existing post-tensioned bridge. Fully grouted, partially grouted, and ungrouted tendon ducts located in actual bridge girders were examined. The results of the impact-echo tests were verified by invasive testing; the ducts were opened up and visually inspected. The impact-echo results correctly located fully grouted, partially grouted, and ungrouted tendon ducts.

Thirty-six panels were tested to investigate the in-plane behavior of grouted concrete masonry under well-defined biaxial tension-compression loading conditions. In the panel tests, stresses are explicitly defined without the need to adopt any assumption of isotropic or elastic behavior. Thus, these tests are shown to be suited to the study of an isotropic characteristics, including cracked masonry and postyielding of reinforcement. The variables considered include the bed joint orientation, the principal stress ratio σ 1 /σ 2 , and the percentages of reinforcement normal and parallel to the bed joints. Modes of failure, strengths, and stress-strain relationships were found to depend on the bed joint orientation and the principal stress ratio. The degree of anisotropy varied, depending on the continuity of grout normal and parallel to the bed joints. Relating the effectiveness of shear reinforcement only to its total percentage was found to be incorrect. The tests showed that relatively large amounts ofshear reinforcement can be beneficial to both shear strength and ductility, if attention is paid to the details and ratios of reinforcement.

This paper gives the results of an experimental investigation to determine the strength and to study the behavior of blockwork masonry columns subjected to axial load. The effects of using different diameters of lateral ties and different percentages of vertical bars were also investigated. A new method to predict the ultimate strength of reinforced blockwork masonry columns was suggested.

Four slab-column subassemblages, modeled after a typical reinforced flat plate building, are tested under combined gravity and lateral loads. The testing program incorporates two levels of gravity loads and compares the effects of biaxial versus uniaxial lateral loading on connection behavior. To study the effectiveness of connection repair, one of the tested specimens is repaired with epoxy/grout and reloaded. The post failure behavior of slab-column connections is investigated and the adequacy of slab reinforcement detailing in preventing progressive collapse is assessed. Existing strength and lateral stiffness models are compared with experimental results. Data from past research are collected to investigate the ductility and drift capacity of slab-column connections. The seismic design of reinforced concrete flat slab buildings is discussed.

Masonry design codes typically allow enhancement of masonry strength beneath a concentrated load due to the strengthening effect of the more lightly stressed surrounding material. This has been verified for solid masonry, but its applicability to face-shell bedded hollow masonry is open to question since failure occurs by splitting of the webs, rather than by vertical cracking. This study investigated the behavior of face-shell bedded hollow concrete masonry subjected to in-plane concentrated loads. A total of 49 wallettes, some plain and others with one- and two-course bond beams, were constructed and subjected to either concentric or eccentric concentrted loads through various-sized loading plates. All wallettes failed consistently by local web-splitting, in a manner similar to hollow masonry subjected to uniaxial compression. The testing program is described together with details of mechanisms of failure, dispersion of load through bond beams, influence of bond beam grout strength, and potential strength enhancement. General implications for the design of hollow masonry subjected to concentrated loads are also discussed, and it is shown that strength enhancement occurs on the basis of loaded length rather than loaded area.