Seismic Behavior of Slender Coupling Beams Constructed with High-Performance Fiber-Reinforced Concrete.

Coupling beams greatly influence the behavior of coupled wall systems. In order to ensure adequate coupling beam behavior under earthquake-induced deformations and stresses, intricate reinforcement detailing is required for reinforced concrete coupling beams, typically in the form of diagonal bars and extensive confinement reinforcement. Such reinforcement detailing, however, creates major construction difficulties. Furthermore, in slender coupling beams, where beam span-to-depth ratios are on the order of 3.0, the effectiveness of diagonal reinforcement is questionable because of its shallow angle (less than 20 degrees) with respect to the beam longitudinal axis. In this study, a design alternative for slender coupling beams that puts less reliance on diagonal reinforcement was experimentally investigated. The use of tensile strain-hardening, high-performance fiber reinforced concrete (HPFRC) as a means to reduce or totally eliminate the need for diagonal bars and substantially reduce confinement reinforcement was evaluated. To validate this design alternative, six precast coupling beams were tested under large displacement reversals. The parameters considered were the coupling beam span-to-depth ratio (2.75 and 3.3), presence of diagonal reinforcement, and material type (HPFRC and regular concrete). Results from large-scale tests indicated excellent damage tolerance, and strength and stiffness retention capacity for slender HPFRC coupling beams. Moreover, tests results showed that diagonal reinforcement can be completely eliminated without a detrimental effect on seismic behavior. The contribution of the HPFRC material to shear strength of the coupling beam was estimated to be on the order of 5*sqrt(fc) (psi) times the cross section area. To simulate the behavior of the tested precast coupling beams under displacement reversals, analytical modeling was conducted using VecTor2, a nonlinear finite element program in which an HPFRC material model can be incorporated. It was found that the behavior of the tested coupling beams could be reasonably predicted in VecTor2. Simulated shear resultant was in good agreement with that of the test specimens. Excluding drift contributed by sliding, which could not be properly captured in VecTor2, drift capacity obtained from the numerical models agreed well with that of the test specimens. Modeling guidelines critical to simulating the seismic behavior of HPFRC coupling beams were also provided.PHDCivil EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/96122/1/monthian_1.pd

Strengthening of damaged low strength concrete beams using PTMS or NSM techniques

This article presents the results of an analytical and experimental study on the performance of rectangular reinforced concrete (RC) beams strengthened using either post-tension metal strapping (PTMS) or side-near surface mounted (SNSM) FRP bars. Four low-strength (15.3 MPa) medium-scale beams were tested in four-point bending in two phases. In Phase I, one control beam was tested up to failure, whereas three beams were tested up to yielding of the main flexural reinforcement. In Phase II, the three pre-cracked beams were strengthened using PTMS or SNSM techniques, and then retested up to failure. The results indicate that the capacity of the pre-cracked PTMS-strengthened beam was only 8 % higher than the control counterpart. Conversely, the SNSM strengthening solution increased the beam capacity by up to 55 %, which is due to additional flexural reinforcement provided by the FRP bars. Moreover, the predictions given by linear cracked sectional analysis and the current ACI guidelines match well the deflection response of the strengthened beams but only up to the yielding load

Performance study of an integrated solar water supply system for isolated agricultural areas in Thailand : a case-study of the Royal Initiative Project

This article presents a field-performance investigation on an Integrated Solar Water Supply System (SWSS) at two isolated agricultural areas in Thailand. The two case-study villages (Pongluek and Bangkloy) have experienced severe draughts in recent decades, and, therefore, water supply has become a major issue. A stand-alone 15.36 kW solar power and a 15 kW solar submersible pump were installed along with the input power generated by solar panels supported by four solar trackers. The aim is to lift water at the static head of 64 and 48 m via a piping length of 400 m for each village to be stored in 1000 and 1800 m3 reservoirs at an average of 300 and 400 m3 per day, respectively, for Pongluek and Bangkloy villages. The case study results show that the real costs of electricity generated by SWSS using solar photovoltaic (PV) systems intergraded with the solar tracking system yield better performance and are more advantageous compared with the non-tracking system. This study illustrates how system integration has been employed. System design and commercially available simulation predictions are elaborated. Construction, installation, and field tests for SWSS are discussed and highlighted. Performances of the SWSS in different weather conditions, such as sunny, cloudy, and rainy days, were analysed to make valuable suggestions for higher efficiency of the integrated solar water supply systems

Prediction of shear strength of reinforced recycled aggregate concrete beams without stirrups

For decades, recycled coarse aggregate (RCA) has been used to make recycled aggregate concrete (RAC). Numerous studies have compared the mechanical properties and durability of recycled aggregate concrete (RAC) to those of natural aggregate concrete (NAC). However, test results on the shear strength of reinforced recycled aggregate concrete beams are still limited and sometimes contradictory. Shear failure is generally brittle and must be prevented. This article studies experimentally and analytically the shear strength of reinforced RAC beams without stirrups. Eight RAC beams and two controlled NAC beams were tested under the four-point flexural test with the shear span-to-effective depth ratio (a/d) of 3.10. The main parameters investigated were the replacement percentage of RCA (0%, 25%, 50%, 75%, and 100%) and longitudinal reinforcement ratio (ρw) of 1.16% and 1.81%. It was found that the normalized shear stresses of RAC beams with ρw = 1.81% at all levels of replacement percentage were quite similar to those of the NAC counterparts. Moreover, the normalized shear stress of the beam with 100% RCA and ρw = 1.16% was only 6% lower than that of the NAC beam. A database of 128 RAC beams without shear reinforcement from literature was analyzed to evaluate the accuracy of the ACI 318-19 shear provisions in predicting the shear strength of the beams. For an RCA replacement ratio of between 50% and 100%, it was proposed to apply a reduction factor of 0.75 to the current ACI code equation to account for the physical variations of RCA, such as replacement percentage, RCA source and quality, density, amount of residual mortar, and physical irregularity

Seismic strengthening of low strength concrete columns using high ductile metal strap confinement : a case study of Kindergarten school in Northern Thailand

The 2014 Chaing Rai earthquake (Thailand) caused extensive damage in many reinforced concrete (RC) buildings built before the introduction of modern seismic design guidelines. Much of the damage on these buildings was attributed to the inadequate capacity and/or ductility of columns. As a result, suitable and cost-effective strengthening techniques for such substandard elements are necessary. This article presents a case study on the seismic strengthening of a one-story RC kindergarten school located in Ampor Pan, Chaing Rai province. The building was partially damaged during the afore-mentioned earthquake, which led to cracking in walls, columns, and beam-column joints. As part of the initial assessment, innovative repair solutions were sought to minimize construction time, labor, and material cost. Accordingly, an innovative strengthening technique that uses Post-tension Metal Strapping (PTMS) was proposed to strengthen the damaged RC elements. This article presents details of the structural assessment performed on the building, as well as details of the PTMS strengthening strategy, which was applied for the first time in a real full-scale structure. This article contributes towards the validation and application of the PTMS strengthening on real structures, which had not been possible until now

High-performance fiber reinforced concrete coupling beams: from research to practice

Results from experimental research that led to the development of a new design of coupling beams constructed with High-Performance Fiber Reinforced Concrete (HPFRC) and simplified reinforcement detailing are presented, along with information related to its implementation in a high-rise building in the city of Seattle, WA. The experimental program consisted of the testing, under large displacement reversals, of a series of large-scale HPFRC coupling beams with span-toheight ratios ranging between 1.75 and 3.3. The main goal of the experimental program was to evaluate the possibility of simplifying diagonal and confinement reinforcement detailing without compromising seismic performance. Experimental results indicate that the use of HPFRC allows the complete elimination of diagonal reinforcement in beams with span-to-height ratios greater than or equal to approximately 2.2. Also, special confinement reinforcement, as used in regular reinforced concrete coupling beams, was found to only be required over a distance of half the beam height from each beam end. For beams with span-to-height ratios smaller than approximately 2.2, a 2/3 reduction in diagonal reinforcement was found to be possible, with the same relaxation in confinement reinforcement as for the more slender coupling beams. Drift capacities of the HPFRC coupling beam specimens, when subjected to shear reversals with amplitudes comparable to the upper shear limit allowed in the ACI Building Code, ranged between approximately 5% and 7% for span-to-height ratios of 1.75 and 3.3, respectively

Punching shear capacity of recycled aggregate concrete slabs

This article investigates the punching shear behavior of recycled aggregate concrete (RAC) two-way slabs. Ten 1500 mm × 1500 mm × 100 mm slabs were tested monotonically. Eight slabs were cast with RAC, whereas two control slabs were cast with natural aggregate concrete (NAC). The RAC incorporated coarse recycled concrete aggregate (RCA) at replacement levels of 25%, 50%, 75% and 100%. Two flexural reinforcement ratios (0.8% and 1.5%) were examined. The results show that the normalized punching shear strength of 100% RAC slabs decreased by 6.5% and 9% compared to NAC slabs for r = 1.5% and r = 0.8%, respectively. Doubling the amount of flexural reinforcement can increase the punching shear capacity of 100% RAC slabs by up to 45%. A punching shear database of 44 RAC slabs from literature and the 8 RAC slabs presented in this study revealed that the punching shear strength of RAC slabs predicted by ACI 318 was conservative, except for slabs with low reinforcement ratios (<0.6%). The punching shear strength predicted by Eurocode 2 gave more conservative results for all levels of RCA replacement and all flexural reinforcement ratios. A yield-line analysis also showed that the failure mode of the RAC slabs was controlled by punching shear

Implementation of High-Performance Fiber Reinforced Concrete Coupling Beams in High-Rise Core-Wall Structures in the Seattle Area

Experimental and analytical studies that led to the incorporation of strain-hardening, high-performance fiber reinforced concrete (HPFRC) coupling beams in the design of a high-rise core-wall structure in Seattle, WA, are described. A total of eight HPFRC coupling beams with span-to-depth ratios ranging between 1.75 and 3.3 were tested under large displacement reversals. The tension and compression ductility of HPFRC materials allowed an approximately 70% reduction in diagonal reinforcement, relative to an ACI Building Code (318-08) compliant coupling beam design, in beams with a 1.75 span-to-depth aspect ratio and a total elimination of diagonal bars in beams with a 2.75 and 3.3 aspect ratio. Further, special column-type confinement reinforcement was not required except at the ends of the beams. When subjected to shear stress demands close to the upper limit in the 2008 ACI Building Code (0.83 f’c [MPa] (10 f’c [psi])), the coupling beams with aspect ratios of 1.75, 2.75 and 3.3 exhibited drift capacities of approximately 5%, 6% and 7%, respectively. The large drift and shear capacity exhibited by the HPFRC coupling beams, combined with the substantial reductions in reinforcement and associated improved constructability, led Cary Kopczynski & Co. to consider their use in a 134 m (440 ft) tall reinforced concrete tower. Results from inelastic dynamic analyses indicated adequate structural response with coupling beam drift demands below the observed drift capacities. Also, cost analyses indicated 20-30% savings in material costs, in addition to much easier constructability and reduced construction time

Torsional strengthening of low-strength RC beams with post-tensioned metal straps : an experimental investigation

This article investigates the behaviour of low-strength reinforced concrete beams under pure torsion with and without strengthening. Four beams were cast and tested in torsion: i) a control beam without vertical reinforcement, ii) two beams with internal stirrups designed for shear and torsion demands using different stirrup spacing (50 and 100 mm), and iii) a beam having steel stirrups with a spacing of 100 mm strengthened using high ductile post-tensioned metal straps (PTMS). The main objective of the PTMS strengthening solution was to investigate the enhancement of torsional strength confined along the beam. The failure modes, torsional capacities, rotation, and strengthening performance in torsion are discussed in in this study. The experimental results indicate that the PTMS improved the cracking torque capacity by up to 15 % compared to the control beam. Moreover, the PTMS also increased the ultimate torque by up to 19 % compared to the unstrengthened beam. Current code equations to predict the torsional capacity of RC beams are also compared with the experimental results. It is found that the predictions obtained by current ACI equation gives a good agreement and yield in general conservative values compared to the experimental ones

Prediction of Shear Strength of Reinforced Recycled Aggregate Concrete Beams without Stirrups

For decades, recycled coarse aggregate (RCA) has been used to make recycled aggregate concrete (RAC). Numerous studies have compared the mechanical properties and durability of recycled aggregate concrete (RAC) to those of natural aggregate concrete (NAC). However, test results on the shear strength of reinforced recycled aggregate concrete beams are still limited and sometimes contradictory. Shear failure is generally brittle and must be prevented. This article studies experimentally and analytically the shear strength of reinforced RAC beams without stirrups. Eight RAC beams and two controlled NAC beams were tested under the four-point flexural test with the shear span-to-effective depth ratio (a/d) of 3.10. The main parameters investigated were the replacement percentage of RCA (0%, 25%, 50%, 75%, and 100%) and longitudinal reinforcement ratio (ρw) of 1.16% and 1.81%. It was found that the normalized shear stresses of RAC beams with ρw = 1.81% at all levels of replacement percentage were quite similar to those of the NAC counterparts. Moreover, the normalized shear stress of the beam with 100% RCA and ρw = 1.16% was only 6% lower than that of the NAC beam. A database of 128 RAC beams without shear reinforcement from literature was analyzed to evaluate the accuracy of the ACI 318-19 shear provisions in predicting the shear strength of the beams. For an RCA replacement ratio of between 50% and 100%, it was proposed to apply a reduction factor of 0.75 to the current ACI code equation to account for the physical variations of RCA, such as replacement percentage, RCA source and quality, density, amount of residual mortar, and physical irregularity