Drilled-in shear reinforcement for concrete thick slabs : modelling aspects

In order to evaluate the performance of drilled-in bonded shear reinforcement, two series of largescale slabs were tested before and after shear strengthening. Experimental results indicate that the 2006 Canadian Standard and the 2010 fib Model Code provisions overestimate the shear strength of such strengthened slabs by about 29% if the drilled-in shear reinforcement is assumed to be totally effective. The main goal of this research is to develop a method for predicting the shear strength of slabs with bonded shear reinforcement. A non-linear finite element model using the program VecTor2 was used to study parameters influencing the slab behaviour up to failure. Results showed that both the behaviour and ultimate strength of slabs are predicted well by the model while taking account of a stress-slip relationship for the bonded reinforcing bars. Moreover, the experimental observations during the loading corroborate the cracking pattern predictions

Experimental and analytical studies of strengthening using drilled-in bonded shear reinforcement

In order to study means of improving the behaviour of thick slabs without shear reinforcement a series of large-scale beams representing thick slabs was constructed and tested. Companion specimens were strengthened using drilled-in reinforcing bars to study the effectiveness of this repair technique. The behaviour of these beams, before and after strengthening, is compared. An additional experimental program using pull-out specimens enabled a study of the bond characteristics of drilled-in reinforcement having different embedment lengths. An analytical model to predict the bond-stress versus slip relationship enabled the development of a method for predicting the influence of the added shear reinforcement in improving the shear strength. These predictions are compared with the experimental results and provide a practical means of assessing the influence of post-installed shear reinforcement

Post-installed shear reinforcement for concrete thick slabs

Many concrete bridges may be associated to a simple thick slabs structural system. With the increase in traffic loads and material degradation, some of these structures need to be strengthened in shear. The goal of this research is to study the behaviour of slabs strengthened with post-installed shear reinforcement and to provide an analytical method of design. The studied reinforcement methods consist in installing rebars into pre-drilled holes in the slab with different anchor systems. The first experimental results showed that shear-strengthened slabs can have failure loads 46% higher than an unstrengthened slab but 29% lower than the Canadian code prediction for conventional stirrups. The VecTor2 finite element analysis tool will be used to study the parameters influencing the slabs behaviour. The first experimental results and associated numerical models outcomes will be presented

Thick concrete slab bridges : study of shear strengthening

Efficient shear strengthening techniques for thick concrete slabs were studied at Université Laval over the last decade. The strengthening techniques consist of adding drilled-in vertical reinforcing bars and to anchor the bars with bolted plates or expansion anchorage at the bar extremities (i.e. the bars are unbonded to the concrete), or to bond the bars to the concrete with high strength epoxy adhesive (no mechanical anchorage). For concrete members with unbonded bars, experimental loading tests and numerical analysis showed that large diagonal shear cracks are required to activate the shear reinforcement and therefore, the shear behaviour of the members is largely influenced by the stiffness of the strengthening. For specimens with epoxy bonded bars, results showed that the development length of the bars is determined by the locations of the shear cracks and thus, bars may debond before reaching their yielding strength. The efficiency of the shear strengthening techniques is therefore largely influenced by the bars spacing and the stiffness of unbonded shear reinforcement

Shear strengthening of thick concrete slabs accounting for loading during strengthening

In order to investigate the effect of the serviceshear load at the time of strengthening a thick slab using bonded transverse reinforcing bars, an experimental study has been carried out.Five (5)beams representing slices of a thick slab were tested to induce different shear load levels in the beamsat the time of strengthening then loaded up to shear failure. Tests were conducted on a slab without shear reinforcement and the others on slabs strengthened at two different load levels at the time of strengthening. The added shear reinforcement was distributed according to two different longitudinal spacings. The results show that,even in the presence of usual service loads, the shear strengthening of thick slabs with bondedbars offers a considerable increase in shear capacity compared to a thick slab without shear reinforcement

Behaviour of thick concrete members with unbonded transverse reinforcement

One commonly used method to increase the shear capacity of existing concrete structures consists of adding vertical steel bars anchored to the structure by means of mechanical anchorages, such as expansion torque controlled anchorages or steel anchorage plates. If the drilled holes are not filled with adhesive then the bars are unbonded along their length. In order to study the behaviour of concrete members with unbonded transverse reinforcement, thick concrete beams (width of 610 mm and height of 750 mm) were loaded until shear failure. It has been observed that their shear capacity is closely related to the shear cracking behaviour. At shear cracking, the propagation of one large diagonal crack is required to activate the vertical unbonded bars, thereby reducing the aggregate interlock shear capacity along the cracks. Beams containing at least minimum amounts of conventional stirrups experience several diagonal cracks at shear failure, whereas a beam with unbonded bars tends to have one dominant crack and can therefore experience the size effect in shear. A finite element (FE) model was also used to study the parameters influencing the behaviour of concrete members with unbonded transverse bars. The finite element results show very good agreement with the experimental results

Behaviour of thick concrete members with unbonded transverse reinforcement

One commonly used method to increase the shear capacity of existing concrete structures consists of adding vertical steel bars anchored to the structure by means of mechanical anchorages, such as expansion torque controlled anchorages or steel anchorage plates. If the drilled holes are not filled with adhesive then the bars are unbonded along their length. In order to study the behaviour of concrete members with unbonded transverse reinforcement, thick concrete beams (width of 610 mm and height of 750 mm) were loaded until shear failure. It has been observed that their shear capacity is closely related to the shear cracking behaviour. At shear cracking, the propagation of one large diagonal crack is required to activate the vertical unbonded bars, thereby reducing the aggregate interlock shear capacity along the cracks. Beams containing at least minimum amounts of conventional stirrups experience several diagonal cracks at shear failure, whereas a beam with unbonded bars tends to have one dominant crack and can therefore experience the size effect in shear. A finite element (FE) model was also used to study the parameters influencing the behaviour of concrete members with unbonded transverse bars. The finite element results show very good agreement with the experimental results

Behavior of epoxy bonded bars in concrete affected by alkali-silica reaction

Installation of drilled-in epoxy-bonded reinforcing bars is generally an effective strengthening method to increase the flexural and shear capacities of deficient concrete structures. However, most of the available studies characterizing the bond behavior of epoxy bonded bars in concrete have been carried out on sound concrete elements—that is, without any pathological material damage. This raises the question of bond capacities in existing damaged elements. This study investigates the influence of alkali-silica reaction (ASR) on the capacity of post-installed reinforcing bars. ASR is a deleterious mechanism that causes expansion and cracking in the affected concrete elements. Pullout tests on post-installed reinforcing bars having embedded lengths of 2db, 4db, and 5db with 15M reinforcing bars (db = 15.9 mm [0.626 in.]) have demonstrated a drop-in bond strength when concrete is affected by ASR. In addition, the study revealed that the progression of concrete expansion due to ASR may lead to some confinement of the post-installed reinforcing bar and possibly increases the bond strength

Design of concrete members strengthened in shear with vertical bonded bars

Due to design using older codes, material degradation and increased traffic loads, numerous reinforced concrete bridge members, such as beams and slabs, have insufficient shear capacity and need shear strengthening. An efficient shear strengthening technique consists of adding drilled-in vertical reinforcing bars within the existing concrete member and to bond these bars to the concrete with high-strength epoxy adhesive. However, the shear design method prescribed by the Canadian Highway Bridge Design Code for members with stirrups may overestimate the shear capacity of shear strengthened members with epoxy-bonded bars. This paper presents the effect of bonded shear reinforcement on shear resistance mechanisms and summarizes a proposed shear design method developed for reinforced concrete members with epoxy-bonded shear reinforcement

Strength and Behavior of Spruce Pine Glulam Timber Moment Connections Using Glued-In Steel Rods

This paper presents experimental testing on glulam beam–column moment-resisting connections using glued-in rods (GiRod) and compares the results with model predictions. Three connection geometries and varying numbers of rods and member size were tested and compared. This experiment will be helpful in grounding research by bringing in new experimental results and proposing an innovative experimentation method. Experimental results showed the high efficiency of glued-in rod connections to transfer loads and bending moment between spruce pine glulam timber members. The observed limit states of the connections were failed steel rods in ductile tensile yielding or wood splitting around the anchorage installed perpendicularly to the grain in the column. It was found that the tested connections behaved as a semirigid moment-resisting connection and exhibited a ductile failure mode when wood splitting was avoided by design. Comparison of experimental results with model predictions showed good agreement, with a deviation under 15% for the moment capacity of the connection