Post-earthquake Performance of a Slab-Column Connection with Punching Shear Reinforcement

Brittle punching failures can occur in slab–column connections due to earthquake-induced unbalanced moments. The performance of undamaged specimens and various repair/strengthening techniques have been studied in the past. This paper investigates a less studied scenario, in which a flat slab–column connection severely damaged by an earthquake is subjected to another earthquake without undergoing repair. The performance under this special loading protocol is analysed. It is shown that the drift capacity was not significantly impaired, but both the lateral and bending stiffness were reduced. Other relevant observations regarding the post-earthquake life of slab–column connections are brought to attention.publishersversionepub_ahead_of_prin

Durability aspects related to rubble stone masonry walls strengthened with reinforced micro-concrete layers

International Seminar on Seismic Risk and Rehabilitation of Stone Masonry Housing, Azores, Portugal, 1998This paper analyses durability aspects related to the use of reinforced micro-concrete as strengthening material of ancient rubble stone masonry walls. The present study is a section of a research project carried out at the New University of Lisbon (Pinho, 2007), to evaluate some structural strengthening solutions for rubble stone masonry buildings. These kind of strengthening solutions, using sprayed micro-concrete layers (shotcrete layers), are very common in Portugal, namely in the rehabilitation of ancient buildings, as may be seen in Azores, after the earthquake of 1998

Experimental research on rubble stone masonry walls

HMC08 - 1st Historical Mortars Conference: Characterization, Diagnosis, Conservation, Repair and Compatibility, LNEC, Lisbon, 24-26 September 2008This paper refers to the results of a research project carried out at Nova University of Lisbon (Pinho [8]), where several experimental models of rubble stone masonry walls were subjected to axial compression and shear-compression tests. The aim of this research project was the experimental evaluation of some structural strengthening solutions for rubble stone masonry buildings. The results of some tests performed to determine physical, chemical and mechanical properties of the constituent materials of the experimental masonry models are also presented. This experimental work was made in cooperation with LNEC, and it was sponsored by some industrial companies

Pull-out and push-in tests of bonded steel strands

Martí Vargas, JR. (2013). Pull-out and push-in tests of bonded steel strands. Magazine of Concrete Research. 65(18):1128-1131. doi:10.1680/macr.13.00061S112811316518Balázs LG .Bond Model with Non-Linear Bond-Slip Law, 1987, Politecnico di Milano, Italy, 395–430, Studi e Ricerche, Post-Graduate Course for Reinforced Concrete Structures, V.8/86.Balazs, G. L. (1992). Transfer Control of Prestressing Strands. PCI Journal, 37(6), 60-71. doi:10.15554/pcij.11011992.60.71Balazs, G. L. (1993). Transfer Length of Prestressing Strand as a Function of Draw-In and Initial Prestress. PCI Journal, 38(2), 86-93. doi:10.15554/pcij.03011993.86.93Balázs, G. L. (2007). Connecting Reinforcement to Concrete by Bond. Beton- und Stahlbetonbau, 102(S1), 46-50. doi:10.1002/best.200710109Carmo RNF .Ancoragem de Armaduras Pré-Esforçadas por Pré-Tensão. MSc thesis, 1999, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Portugal, (in Portuguese).Faria, D. M. V., Lúcio, V. J. G., & Pinho Ramos, A. (2011). Pull-out and push-in tests of bonded steel strands. Magazine of Concrete Research, 63(9), 689-705. doi:10.1680/macr.2011.63.9.689Faria, D. M. V., Lúcio, V. J. G., & Ramos, A. P. (2011). Strengthening of flat slabs with post-tensioning using anchorages by bonding. Engineering Structures, 33(6), 2025-2043. doi:10.1016/j.engstruct.2011.02.039Faria, D. M. V., Lúcio, V. J. G., & Pinho Ramos, A. (2012). Post-punching behaviour of flat slabs strengthened with a new technique using post-tensioning. Engineering Structures, 40, 383-397. doi:10.1016/j.engstruct.2012.03.014Laldji S .Bond Characteristics of Prestressing Strand in Grout. MPhil thesis, 1987, University of Leicester, UK.Laldji, S., & Young, A. G. (1988). Bond between steel strand and cement grout in ground anchorages. Magazine of Concrete Research, 40(143), 90-98. doi:10.1680/macr.1988.40.143.90Lopes, S. M. R., & do Carmo, R. N. F. (2002). Bond of prestressed strands to concrete: transfer rate and relationship between transmission length and tendon draw-in. Structural Concrete, 3(3), 117-126. doi:10.1680/stco.2002.3.3.117Martí-Vargas, J. R., Serna-Ros, P., Fernández-Prada, M. A., Miguel-Sosa, P. F., & Arbeláez, C. A. (2006). Test method for determination of the transmission and anchorage lengths in prestressed reinforcement. Magazine of Concrete Research, 58(1), 21-29. doi:10.1680/macr.2006.58.1.21Marti-Vargas, J. R., Arbelaez, C. A., Serna-Ros, P., Navarro-Gregori, J., & Pallares-Rubio, L. (2007). Analytical model for transfer length prediction of 13 mm prestressing strand. Structural Engineering and Mechanics, 26(2), 211-229. doi:10.12989/sem.2007.26.2.211Palmer, K. D., & Schultz, A. E. (2011). Experimental investigation of the web-shear strength of deep hollow-core units. PCI Journal, 56(4), 83-104. doi:10.15554/pcij.09012011.83.10

Development of steel angles as energy dissipation devices for rocking connections

This paper focuses on the development of energy dissipaters for rocking precast systems. The energy dissipaters developed in this work are to be used externally, having the advantages of being easy to inspect and replace after an earthquake. The main parameters to take into account for the development of the energy dissipaters are the cyclic behavior, the strength, and the ductility. The cyclic behavior has to be stable from cycle to cycle. The developed dissipater has to respond with adequate strength. The ductility is also important as the dissipater has to sustain the displacements applied by a major seismic event without failure. For this purpose, the experimental campaign using steel structural angles as dissipaters is described and solutions able to deliver the desired behavior are shown. To support and complement the experimental tests, two-dimensional numerical models using a finite element software are shown and an analytical method is also presented to describe the behavior in both elastic and plastic ranges and thus design the elements. In both cases, good agreement with the experimental results is achieved. The analytical method has the advantage of being easy to implement for estimation of the steel angle response

Innovative Seismic Strengthening Techniques to Be Used in RC Beams’ Critical Zones

The seismic performance of a structural frame system can be enhanced by strengthening the RC beams’ critical zones. In this paper is presented an experimental study on the improvement of the beam behaviour, subjected to an alternative cyclic procedure which considers the gravity loads reflecting the real demands on the beams’ critical zone. Two strengthening solutions are presented: unbounded post-tension (PT) tendon strengthening to increase resistance and limit residual deformations, and unbounded post-tensioning with jacketing of the RC beam with unidirectional fibre mat reinforced grout (UFRG) to limit compression damage, improving section confinement, thus delaying concrete crushing and buckling of longitudinal reinforcement. The original UFRG material was developed within this study, to apply as a small thickness jacketing material for strengthening RC structures. The main idea was that the steadiness provided by preplacing continuous fibre mats into the mould reduced the fibres’ segregation tendency during the high-performance grout pouring and allowed for the optimisation of their percentage and alignment, attaining a higher tensile strength. The experimental response of the tested Specimens is presented and evaluated through performance parameters that are properly discussed and adjusted to the alternative cyclic procedure. Finally, theoretical predictions are presented, and an adjustable multilinear model is proposed to estimate the strengthening solution’s response

Reversed horizontal cyclic loading tests of flat slab specimens with studs as shear reinforcement

Erasmus Mundus Action 2, Grant/Award Number: 2014-0848/001-001The results of a series of experiments on four reinforced concrete flat slab specimens with shear studs and a control specimen without any shear reinforcement are presented. The specimens were tested under constant gravity loads and reversed horizontal cyclic displacements. The main test variables were the applied gravity load and the number of perimeters of studs. One of the specimens was tested in two phases to study the postearthquake behavior. Results showed a considerable improvement of the deformation capacity of specimens with studs compared to the reference specimen. In agreement with previous research, increasing the applied gravity shear ratio resulted in a lower experimental drift capacity. It is shown that a better explanation of the observed ultimate drifts can be made by considering also the flexural capacity and the extent of shear reinforcement. The specimen tested in two phases exhibited considerable residual capacity, even after severe horizontal loading.authorsversionpublishe

Performance assessment of flat slabs strengthened with a bonded reinforced-concrete overlay

Punching strengthening of reinforced-concrete slabs using a bonded reinforced-concrete overlay (BRCO) is an efficient alternative to traditional strengthening systems such as post-installed shear reinforcement, enlargement of the support column, or bonded fibre-reinforced polymer strips. The BRCO technique allows for both the flexural stiffness and shear strength of existing slabs to be increased. Shear strength increases due to the greater slab thickness, while an increase in flexural stiffness is also provided by the added reinforcement. Particular attention must be paid to the interface between the existing slab and the BRCO, because performance gains can only be achieved if the existing slab and the new concrete layer work monolithically. Interface performance can be improved through surface preparation and mechanical connectors; the latter is recommended to avoid premature debonding failure. This paper presents an ad hoc design approach for flat slabs strengthened with BRCO based on the critical shear crack theory, which accounts for slab rotation after strengthening. This is a fundamental parameter to assess the punching capacity of the strengthened slab. The efficiency of the proposed method is confirmed by the agreement between analytical results and experimental data collected during an experimental campaign carried out at the Universidade Nova de Lisboa.preprintpublishe

Slab–column connection punching and ductility improvement methods for seismic response of buildings with flat slabs

TDC/ECI‐EST/30511/2017 EXPL/ECM‐EST/1371/2013 EXPL/ECM‐EST/1371/2013 PTDC/ECI‐EST/30511/2017Replicating boundary conditions of slab–column connections under seismic loading in a realistic manner is difficult, and different test setups have been used throughout the years. An innovative test setup has been developed at NOVA School of Science and Technology, and it has been used to test various punching shear behavior enhancement methods, including stirrups, headed studs, fiber-reinforced concrete (FRC), high-strength concrete (HSC), and post-installed bolts under similar conditions. The aim of this paper is to compare the results from these different solutions for seismic loading. It is shown that relatively large drift ratios at failure can be achieved in slabs containing shear reinforcement. However, less conventional methods such as FRC and HSC are shown to be promising alternatives. Compared to reference specimens that failed at 1% drift, the other specimens with various enhancement methods achieved significantly higher drifts, ranging from 2.5% to above 6.0%.authorsversionpublishe

Long term application of bus monitoring system to short and medium span bridges and damage detection

In this study, as one solution to the problem for condition assessment of existing short and medium span reinforced/prestressed concrete bridges, a new monitoring method using a public bus as part of a public transit system (bus monitoring system) is proposed, along with safety indices, namely, characteristic deflection, which is relatively free from the influence of dynamic disturbances due to such factors as the roughness of the road surface, and a structural anomaly parameter. A basic study was conducted by using the results of technical verification experiments and numerical analysis simulation. This paper describes the details of not only how to assess the bridge condition by public bus vibration measured in operating on Ube City bus network as a specific example for verify the system but also what kind of consideration we need to apply the system to existing bridges in overseas country.publishersversionpublishe