Near Surface Mounted Research Articles

Flexural response of FRP-strengthened lightweight RC beams: hybrid bond efficiency of L‐shape ribbed bars and NSM technique

This paper presents the results of an experimental study on employing near surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement technique, and L‐shape ribbed bars, for flexural strengthening of lightweight reinforced concrete (RC) beams. 18 RC beams including 14 lightweight RC beams and four normal-weight concrete beams were designed. The beams were strengthened with glass fiber-reinforced polymer (GFRP) bars and carbon fiber-reinforced polymer (CFRP) laminate in bending tests. Test parameters included: (1) different FRP materials (glass bars and carbon sheets), (2) longitudinal steel reinforcement ratio, and (3) type of strengthening technique used (NSM reinforcement or hybrid). The ultimate tensile strength, deflection, compressive and tensile strain of concrete, and failure mode of the beams were examined under four-point flexural test. Results showed that the ultimate strength of all RC beams increased between 33 and 105% compared to the control beam. The ultimate strength of beams reinforced with CFRP in the mid-span region was 10% higher than that of beams strengthened at both ends, although the former exhibited 28% lower ultimate deflection. The ultimate strength and deflection of RC beams strengthened with combined steel reinforcing bars and GFRP bars were 10% and 108% higher, respectively, compared to those of RC beams strengthened with GFRP bars only. Hybrid L‐shape ribbed bars beams showed a considerably higher ductility (up to 170% increase in the ultimate deflection) compared to other beams. The comparison of the experimental results of the ultimate strength of the beams with ACI440-2R guidelines indicated a reasonable and conservative prediction of the code expression.

Experimental Study on Effects of Additional Prestressing Using Fiber Reinforced Polymers and Strands on Deterioration of PSC Bridge Structure.

Concrete bridge structures require reinforcement, as their performance deteriorates over time. In this regard, this study evaluated the effect of additional prestressing using fiber-reinforced polymers (FRPs) and strands applied to a demolished, deteriorated bridge. In particular, specimens were prepared for a bridge subjected to non-, near-surface mounted (NSM), and external prestressing (EP) strengthening to evaluate the stiffness and safety of the structure. In the 200–400 kN load range, the EP method exhibited the highest stiffness (15 kN/mm), followed by non-strengthening (8.5 kN/mm) and the NSM method (5.45 kN/mm). The EP method increased the stiffness by approximately two times; however, the NSM method decreased the stiffness by 0.6 times. In the 400–800 kN load range, the EP and NSM methods yielded stiffness values of 2.58 and 0.7 kN/mm, respectively. These results confirm that the EP method reinforces the structure. The results of this study are expected to be used as basic data to reinforce deteriorated bridges in actual operation.

Experimental and numerical investigation on strengthening of RC flat slabs with central opening

Slab openings occur quite often in practice to provide a convenient path for utility ducts. However, introducing an opening into a reinforced concrete flat slab causes local cracking in the vicinity of the opening leading to a reduction in stiffness and capacity of the slab. In this paper, different methods of strengthening flat slabs with central openings are investigated experimentally and numerically. The experimental program consists of six slab specimens with dimensions of (1100 × 1100 × 100) mm with cut out openings of (300 ×300) mm. Two slabs were considered as reference specimens and tested without strengthening; one of them had no opening, and the second had a central opening. The remaining four slabs had openings and were strengthened with different techniques. These include adding Near Surface-Mounted (NSM) steel bars, steel strips with anchor bolts, carbon fiber laminates (CFL), and an overlay of engineered cementitious composite (ECC) material reinforced with welded wire mesh. The results show that using different strengthening techniques leads to an increase in load-carrying capacity for all the strengthened slabs. The reinforced ECC overlay strengthening method achieved the largest increase in the capacity by 31% compared to the reference slab with central opening. The finite-element analysis is carried out to validate the experimental results. Good agreement between the finite-element analysis and the experimental results is obtained confirming many of the findings of this study.

Seismic performance of circular RC columns strengthened in flexure using NSM reinforcement and externally bonded BFRP sheets

To study the seismic performance and recoverable capacity of reinforced concrete (RC) columns strengthened in flexure by employing different kinds of reinforcing materials, six 1/4.7 scale circular specimens including one control, which were strengthened by combining near-surface-mounted (NSM) reinforcement with externally bonded basalt fiber reinforced polymer (BFRP) sheets, were designed to investigate the seismic behavior and tested under the constant axial compressive load and lateral cyclic loading. The experimental parameters included different types of NSM reinforcing materials (carbon or basalt fiber reinforced polymers, steel), confinement conditions (no wrapping and wrapping), and different types of externally bonded BFRP sheets (unidirectional and bidirectional BFRP sheets). The results demonstrate that.the scheme of NSM reinforcement is an effective solution toward enhancing the flexural capacity and the recoverable performance of RC columns. Compared to the other strengthening schemes, the scheme (column C3-10B-4U) combining NSM BFRP bars with externally bonded BFRP unidirectional sheets is most effective in increasing the elastic energy dissipation capacities and also enhancing the ductility and deformation capacity of strengthened columns, but do not change the stiffness significantly. Furthermore, the results indicate that the residual displacement of the column C3-10B-4U is the smallest of all columns under the same applied displacement and thereby the recoverability of the column C3-10B-4U was better than that of the other strengthened columns.

Experimental and numerical investigation on low-strength RC beams strengthened with side or bottom near surface mounted FRP rods

This article examines experimentally and numerically the flexural performance of low-strength reinforced concrete (RC) beams strengthened using near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) rods. Five RC rectangular beams were tested in four-point bending until failure. Four of these beams were strengthened using Bottom NSM (BNSM) or Side NSM (SNSM) rods. The results are discussed in terms of observed damage, load capacity, and midspan deflection. It is shown that the SNSM strengthening solution enhanced the cracking load of the beams by up to 19%. Similarly, the yield and ultimate load-carrying capacities of the strengthened beams increased by up to 31% and 64%, respectively. It is also shown that moment-curvature and FE approaches predict well the deflections of the strengthened RC beams within 20% and 10% of accuracy at failure. The results from nonlinear Finite Element (FE) analyses showed a better agreement with the experimental results up to failure (within a 10% of accuracy). For the beams presented in this study, the crack widths calculated by Eurocode 2 match reasonably well the measured values.

Flexural strengthening of RC beams with NSM-GFRP technique incorporating innovative anchoring system

Reinforced concrete (RC) beams may require flexural strengthening due to the corrosion of reinforcing bars or changes in the design load. The near surface mounted (NSM) and externally bonded (EB) techniques, using either glass or carbon fibre-reinforced polymer (GFRP or CFRP) composites, are used for strengthening deficient RC beams. However, RC beams strengthened with both techniques are susceptible to the debonding failure of the FRP composites. This paper proposes an innovative anchoring system for NSM strengthening of the RC beams, which comprises an L-shaped GFRP bar anchor (L-anchor), U-shaped CFRP strips (U-strips) and double plate (DP-anchor). The developed strengthening technique is termed as NLUD technique. Seven RC beams were cast and tested under four-point bending. The experimental results showed that RC beams strengthened with the NLUD technique achieved significantly higher flexural load. The NLUD technique prevented the debonding failure of GFRP bars of the strengthened RC beams.

Fire behaviour of CFRP-strengthened RC slabs using different techniques – EBR, NSM and CREatE

This paper presents an experimental study about the fire behaviour of reinforced concrete (RC) slabs strengthened with carbon fibre reinforced polymer (CFRP) strips, applied according to three different techniques: externally bonded reinforcement (EBR); near-surface mounted (NSM), and continuous reinforcement embedded at the ends (CREatE), a new technique that prevents premature CFRP debonding. The main goals of this study were three-fold: to understand and compare the fire behaviour of the strengthening techniques, namely the CREatE technique (yet to be studied); to assess the efficiency of the fire protection schemes (constant thickness vs. increased thickness at the CFRP anchorage zones) in extending the fire resistance of the CFRP systems; and, based on the experimental results and data available in the literature, to propose “critical” temperatures for the fire design of CFRP-strengthened RC members. The results obtained show that: (i) without protection, the CREatE technique presented higher fire resistance than the alternative NSM and EBR techniques (24 min vs. 16 min and 2 min); (ii) with fire protection, regardless of its geometry, the NSM and CREatE techniques presented a similar fire resistance (both above 120 min), higher than the EBR technique (less than 60 min); and (iii) the “critical” temperatures for each technique were defined as 1.0Tg, 2.5Tg and 3.0Tg for EBR, NSM and CREatE, respectively, with Tg being the glass transition temperature of the adhesive, defined based on the onset of the storage modulus curve decay from dynamic mechanical analysis.

Reinforced Concrete Beams Strengthened in Flexure with Near-Surface Mounted 7075 Aluminum Alloy Bars

The flexural behavior of reinforced concrete (RC) beams strengthened with near-surface mounted (NSM) 7075 aluminum alloy (AA) bars was investigated through experimental testing. In particular, 10 RC beams strengthened with NSM AA bars and one control beam were tested under four-point bending loading. The experimental variables included NSM reinforcement ratio, bonded length of NSM reinforcement, end anchoring of NSM reinforcement, and type of bonding agent. The test results were evaluated in terms of the load-deflection curves, failure modes, ductility, and strains in NSM reinforcements, and the effects of different test parameters on the effectiveness of the proposed strengthening approach were discussed. In addition, analytical models were developed to predict the load-bearing capacities of strengthened beams failed by intermediate crack debonding and concrete cover separation, respectively. The RC beams strengthened with NSM AA bars exhibited a significant improvement in maximum load ranging from 35% to 120% over the reference specimen.

Models for Predicting Strength of RC Columns Strengthened with NSM-CFRP Strips and CFRP-Fabric Wraps

A comprehensive experimental investigation was carried out on reinforced concrete (RC) columns strengthened with near surface mounted (NSM) Carbon fiber reinforced polymer (CFRP) strips with CFRP fabric wraps as confinement. The number of NSM-CFRP strips and the number of CFRP-Fabric wraps were varied. The RC columns were subjected to concentric and eccentric loads with different eccentricities that resulted in uniaxial bending. Significant improvements in strength and ductility were observed in the strengthened columns compared to that of the control specimen. In this investigation four empirical models, based on the experimental results, were developed to predict the un-strengthened and the NSM-CFRP strengthened RC columns using different parameters. The capacities of the columns predicted by the developed empirical models were validated using the obtained experimental results. It is observed that the developed empirical models have exponential decay and a near-perfect fit to the experimental results, with R2 averaging more than 99% and an average mean absolute percent error (MAPE) of 6.6%. It is concluded that the developed models can be used as useful tools for predicting capacity of columns with NSM-CFRP strips and CFRP wraps under axial loading and uniaxial bending.

Modeling the behavior of CFRP-strengthened RC slabs under fire exposure

This paper presents the development of a numerical model that simulates the fire response of reinforced concrete (RC) slabs externally strengthened with carbon fiber-reinforced polymer (CFRP)laminates using two different techniques, externally bonded (EB) and near-surface mounted (NSM). A three-dimensional (3D) nonlinear finite element (FE) model is developed to predict the thermal and structural behavior of strengthened RC slabs subjected to fire. The model incorporates temperature-dependent thermal and mechanical properties of concrete, steel reinforcement, and CFRP, as well as mechanical bond interaction between CFRP and concrete interfaces. The predicted temperature profiles, ultimate loads, and midspan deflections are compared with previously published experimental data. Results from the proposed model show a good correlation with the experimental data throughout the fire exposure duration. The validated model can be adapted to conduct parametric studies intended to inspect the effect of important factors that influence the behavior of strengthened RC slabs under fire.

Finite element modelling of RC beams strengthened in flexure with NSM FRP and anchored with FRP U-jackets

Reinforced concrete (RC) beams flexurally-strengthened with near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars/strips have been frequently found to fail by debonding at the end of NSM FRP. Such end debonding failures significantly limit the performance of the strengthened beams and the utility efficiency of FRP material. To mitigate/prevent the debonding failures of NSM-strengthened beams, the adoption of FRP U-jackets is an attractive option. A systematic experimental study on RC beams flexurally-strengthened with NSM carbon fibre-reinforced polymer (CFRP) strips and anchored with FRP U-jackets have been conducted and presented by the authors in a previous study. In order for a better and in-depth understanding of the behaviour of such RC beams and for the development of reliable design code/guideline in the future, an accurate finite element (FE) model for such RC beams is proposed in this paper. In the proposed nonlinear FE model, the material properties and bond-slip relationships were properly defined. The failure modes, load–deflection responses and strain development of the beams obtained from FE predictions and test observations were carefully compared. It was shown that the proposed FE model is capable of providing accurate predictions to the test results.

Behavior of RC Beams Strengthened with NSM-CFRP Strips Subjected to Fire Exposure: A Numerical Study

The use of Near-Surface Mounted (NSM) Carbon-Fiber-Reinforced Polymer (CFRP) strips is an efficient technology for increasing flexural and shear strength or for repairing damaged Reinforced Concrete (RC) members. This strengthening method is a promising technology. However, the thin layer of concrete covering the NSM-CFRP strips is not adequate to resist heat effect when directly exposed to a fire or at a high temperature. There is clear evidence that the strength and stiffness of CFRPs severely deteriorate at high temperatures. Therefore, in terms of fire resistance, the NSM technique has a significant defect. Thus, it is very important to develop a set of efficient fire protection systems to overcome these disadvantages. This paper presents a numerical study that investigates the fire behavior of thermally insulated RC beams flexurally strengthened with NSM-CFRP strips and subjected to fire exposure according to the ISO 834 standard. The numerical study considered three-dimensional finite element models in the ABAQUS software that have been developed to simulate and predict the performance (thermal and structural response) of fire endurance tests on strengthened, uninsulated strengthened, and thermally insulated beams strengthened with NSM-CFRP strips, which were exposed to fire and had different fire insulation schemes. The insulation used was plaster from local material with a thickness range of 25 to 50mm. The variation of the thermal and mechanical properties with the temperature of the constituent materials was considered. All beams' mechanical and thermal responses were adequately simulated using numerical models. The results of the numerical simulations were in good agreement with the experimental data. The fire behavior of the NSM-CFRP strengthened RC beams was examined and particularly the efficiency of the NSM strengthening system during the fire. The behavior in the fire of the NSM-CFRP strengthening system on the RC beams thermally protected with different fire insulation schemes was assessed. Finally, the effectiveness of fire insulation was studied.

Experimental and theoretical analyses of the progressive collapse resistance of NSM strengthening RC frames after the failure of a corner column

When exposed to accidental loads, reinforced concrete (RC) frames are vulnerable to progressive collapse after the failure of a corner column, so necessary strengthening schemes should be employed for the frame. By strengthening the slab with near-surface-mounted (NSM) glass fiber-reinforced polymer (GFRP) bars and engineered cementitious composites (ECC) layer, this study experimentally revealed the effect of the strengthening method on the progressive collapse behavior of beam-slab systems after the removal of a corner column. Then, on the basis of experimental results, a theoretical analysis method of the peak capacity for the beam-slab system is proposed according to the principle of virtual work and the yield-line theory. The derived formula can accurately predict the progressive collapse resistance of the RC beam-slab system after the failure of a corner column and quantitatively evaluate the contribution of floor slabs to the structural capacity. The validity of the method is also proven by the application to the structural capacity of a flat-slab system and a beam-column system. Finally, according to the theoretical formula, the influence of several parameters on the structural capacity is investigated, such as the earthquake fortification intensity of the frame, the over-strength factors, the column spacing, and the depth-to-span ratio of the beam. The research results demonstrate that after considering the L-beam action, the capacities of the test specimens can be improved by 52%–65%. The capacity of the flat-slab system is the lowest among the above three structural systems. The structural progressive collapse resistance can be effectively improved through enhancing the constraint stiffness of the corner beam-column joint and utilizing building materials with high plastic development ability.

Experimental and Numerical Investigations on the Behavior and Failure Mechanism of RC Beams Strengthened with Near-Surface Mounted High-Strength Aluminum Alloy Bars

This paper presents experimental and numerical investigations on the flexural behavior of reinforced concrete beams strengthened with near-surface mounted high-strength aluminum alloy (AA) bars subjected to four-point bending load. A total of five RC beams, including one control beam and four beams strengthened using near-surface mounted (NSM) AA bars with or without CFRP U-warp end anchorage, were constructed and tested monotonically up to failure. To get a better understanding of the flexural behavior and failure mechanism of the tested specimens, 3D finite element models were developed. A comparison between the finite element (FE) and experimental results was carried out and therefore confirmed the ability of the developed FE models to accurately predict the flexural performance of the RC beams strengthened with NSM AA bars. In addition, FE simulations provided an in-depth investigation of the intermediate crack-induced debonding (ICD) and concrete cover separation (CCS) failures. It is observed from the experimental and FE results that compared to the control specimen, more than 34% increase in the load-carrying capacity of the NSM strengthened specimens was achieved. In addition, the CFRP U-wrap end anchorage contributed to the prevention or delay of the CCS and ICD failures and hence increased the load-carrying capacity and enhanced the displacement ductility of the strengthened beam specimens. Furthermore, a FE parametric study was carried out to investigate the influence of different parameters on the performance of the RC beams strengthened with NSM AA bars, and recommendations based on the parametric study for efficient application of the NSM strengthening technique were given.

Prediction of the seismic behavior of concrete beams strengthened with aluminum alloy bars and/or basalt fiber‐reinforced polymer bars

SummaryThis paper investigated the seismic performance of reinforced concrete (RC) beams strengthened with aluminum alloy (AA) rods and/or basalt fiber‐reinforced polymer (BFRP) rods using the near‐surface mounted (NSM) technique under a low‐cycle reversed loading test. A numerical calculation procedure was presented based on the strain compatibility and static equilibrium principles for estimating the moment–curvature response of these strengthened beams. The bending deflection and shear deflection were determined by the curvature distribution and shear strain distribution along the beam length, respectively. The results showed that the strengthened beams experienced three failure modes: intermediate crack‐induced debonding (ICD), critical diagonal crack (CDC) debonding, and concrete cover separation (CCS). Increasing the number of strengthening bars on each side significantly enhances the load‐carrying capacity of the beams strengthened with either AA or BFRP bars. The predictive accuracy of the proposed methodology was evaluated by comparing the predicted load‐carrying capacities and deflections to the test characteristic points. The proposed theoretical model provided good verification of the load‐carrying capacities and deflections with high accuracy.

Experimental investigation of strengthening of RC one-way slabs using NSM and hybrid techniques under impact loading

Reinforced concrete (RC) slabs are often subjected to impact loads. Due to a relatively low tensile strength and energy dissipating characteristics, the impact resistance of slabs is considered poor. Over the last few years, strengthening RC slabs with externally bonded reinforcement (EBR) methods has become a conventional technique. In this paper, six RC one-way slabs are prepared and experimentally investigated under impact loading. Since failure in slabs under impact loadings was in the form of punching shear, two new techniques are proposed to strengthen slabs against impact loads. These techniques include near surface mounted (NSM) and hybrid with high strength reinforcement (HSR) bars and carbon fibre reinforced polymer (CFRP) strips in the form of transverse, longitudinal and diagonal strengthening methods. The experimental results demonstrated that the above-mentioned strengthening techniques in one-way slabs lead to a change in the type of failure, the change of crack patterns and slabs failure. The mentioned strengthening methods lead to an increase of load carrying capacity and increase of dissipated energy.

NLFE modeling of bond between NSM CFRP strips and heat-damaged concrete

A nonlinear finite element (NLFE) model was developed to describe bond behavior between heat-damaged concrete and near-surface mounted (NSM) fiber-reinforced polymer (FRP) strips. The different components of near-end pullout specimens were represented using proper elements in ABAQUS software with the cohesive element adopted to consider bond behavior. The model is calibrated using data from two published experimental works, before its predictions were extrapolated to consider the effect of temperatures (23–550 °C), along with the effects of concrete strength (25–55 MPa), bond length (100–350 mm), spacing (50–200 mm) and fiber type of NSM CFRP strips. Elevated temperatures, in excess of 300 °C, caused a reduction in residual pullout force, yet an increase in bond ductility. The degradation in bond was more pronounced for specimens with higher-grade concrete and lower spacing between strips. Exposing concrete blocks to 450 °C and above undermined the contribution of NSM CFRP strips (100–350 mm) to bond strength. The type of composite had a minor (if any) impact upon bond behavior between heat-damaged concrete and FRP strips for temperatures higher than 300 °C. The NLFE cracking patterns indicated that bond failure mode in the pullout specimens is dictated by the spacing between strips with minimal impact of exposure temperature or bond length.

Structural behavior of RC beams strengthened with prestressed near surface mounted technique using basalt FRP bars

This research aimed at studying the flexural behavior of RC beams strengthened with near surface mounted (NSM) technique using basalt FRP (BFRP) bars to assess their efficiency for strengthening RC beams in order to be introduced as an alternative to other types of FRP bars. Moreover, this study investigated a new type of strengthening technique, named prestressed near surface mounted (PNSM) technique, which is expected to offer lots of advantages owing to combining two well-known “external prestressing” and “NSM” techniques. The variables considered in this study were the strengthening effect (unstrengthened and strengthened), the type of the FRP bars (BFRP and GFRP), the strengthening technique (NSM and PSNM), the initial prestressing level (30% and 50% of ultimate tensile capacity of BFRP bars), and the position of NSM FRP bars (bottom and side). The test results demonstrated the efficiency of using BFRP bars for strengthening RC beams with NSM and PNSM techniques. Additionally, BFRP bars offered additional advantage compared to GFRP bars when strengthened with PNSM technique owing to its higher creep rupture strength. Moreover, the test results proved that strengthening of RC beams with PNSM technique offers superior enhancement in the pre-cracking stage compared to NSM technique while sacrificing a great portion of beam’s ductility.

New type of CFRP reinforcement and technique for the flexural strengthening of RC balconies

The present work assesses the potentialities of a new carbon fibre reinforced polymer (CFRP) bar, applied according to a hybrid technique for the flexural strengthening of cantilever type reinforced concrete (RC) structures, such as the case of RC balconies. The CFRP bar is formed by an inclined extremity that is inserted into a hole according to the embedded through section (ETS) technique, a part that is applied according to the near-surface mounted (NSM) technique, and a transition zone between these two parts. The anchorage conditions of the ETS part of the CFRP bar allow limiting the strengthening intervention to the cantilever zone of the balcony, with an almost null intrusion to the interior of the building.The effectiveness of this CFRP reinforcement and technique was assessed by testing 9 double-sided RC balcony prototypes, in a total of 18 tests. The inclination of the ETS part of the CFRP bar (15° and 30°), the concrete strength class (C25 and C35) and the ratio of existing flexural tensile reinforcement (ρls=0.28% and 0.44%) were the variables investigated in terms of flexural strengthening performance. The results showed that the strengthening effectiveness has increased with the decrease of the inclination of the ETS part of the CFRP bar. A reinforcement ratio of 0.17% of CFRP bars with an extremity at 15° inclination, has doubled the load-carrying capacity of the corresponding reference prototypes.The applicability of the most recent formulation of the fib bulletin 90 for the flexural strengthening of RC elements with NSM CFRP reinforcements was assessed for this type of application. The ratio between maximum load registered experimentally and predicted with fib formulation was 0.95 with a standard deviation of 0.08. However, this high level of predictive performance requires the effective tensile strength of the transition zone of the CFRP bar to be known, which is still a critical aspect of the current generation of CFRP bars. A numerical approach was developed, capable of estimating the force–deflection, the strains and stresses in the constituent materials and evolution of stiffness degradation of the strengthened structures during the loading process, and its high predictive performance was also demonstrated by simulating the experimental tests carried out.

Evaluation of Effective Polymer Fiber Length on Energy Absorption Capacity of Reinforced Beams by EBR and NSM Methods

This study presents a comparison of two methods used for retrofitting Reinforced Concrete (RC) beams, namely, the Externally Bonded Reinforcement (EBR) and the Near-Surface Mounting (NSM) methods. A parametric analysis was carried out using variables such as the retrofitted, the retrofitting method (EBR and NSM), and the thickness of the Carbon Fiber-Reinforced Polymer (CFRP) sheets. To achieve this goal, the finite element method and ABAQUS software were employed. An un-retrofitted beam was also simulated as the control specimen for comparison. Beam responses were compared through load–displacement and energy absorption capacity diagrams. Results show that the higher energy absorption capacity in all CFRP-retrofitted RC beams, which was 1.69–5.54 times higher than in un-retrofitted beams. In the case where half of the beam was reinforced using CFRP sheets, the entire beam assembly and the CFRP sheet contributed to load-bearing, thus delaying crack nucleation in the beam and increasing its energy absorption capacity. As a result, the energy absorption capacity of the beam, in this case, was less than that obtained in the previous one where half the span of the beam was retrofitted.