Seismic Performance of Reinforced Concrete Buildings with Joist and Wide-Beam Floors during the 26 November 2019 Albania Earthquake

Publisher Copyright: © 2023 by the authors.Beams with width greater than their depth and depth equal to the depth of the slab (concealed wide beams) are widespread in Reinforced Concrete (RC) buildings in Albania. A large number of RC buildings with wide beams were hit by a strong Mw6.4 earthquake on 26 November 2019. The earthquake hit two of the most densely populated areas in Albania and caused widespread damage to these buildings. This paper aims to provide an updated view on the seismic performance of buildings with wide beams in light of the new field data following the 26 November 2019 Albania earthquake. To this end, a thorough literature review including experimental and field observations from past earthquakes is presented and data from field visits in Albania are described. It was found that damage to the joists and wide beams themselves was limited, even when the buildings suffered significant non-structural or structural damage in other elements as a result of the earthquake. A discussion on the behavior of wide beam–column frames based on nonlinear structural analyses and tests from the literature is presented. Furthermore, the implications of the results of the analysis for the seismic performance of RC buildings are discussed and confronted with observations from the 2019 Albania earthquake. Based on the literature review, further experimental research on wide beams with longer and more realistic span lengths is recommended.publishersversionpublishe

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

Comportamento de Lajes Fungiformes Sujeitas a Acções Horizontais Cíclicas

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Punching of reinforced concrete flat slabs – Rational use of high strength concrete

PTDC/ECI-EST/30511/2017; SFRH/BD/76242/2011; The authors are grateful to CIMPOR for providing the cement and Sika for providing VISCOCRETE 20HE and SIKACRETE HD.This paper deals with punching of reinforced high strength concrete (HSC) flat slabs. Despite the use of HSC increased significantly in the last years, the experimental research on punching behavior of HSC slabs is still limited. Furthermore, most of this past research adopted concrete compressive strength lower than 90 MPa. In a previous work by this research group three specimens with concrete compressive strength around 120 MPa and one with normal strength concrete (NSC) were tested. The present work represents the continuation of the previous activity and it is focused on the rational use of HSC. Four specimens with HSC and one of NSC were tested under monotonic vertical loading. The HSC was placed only in the slab-column connection region and it was limited to a thin layer in the compressive zone, in order to have a more economical and sustainable solution. This rational use of the HSC showed excellent results in terms of punching strength. Limiting the HSC to a thin layer in the compressive zone resulted in an almost equal punching strength to that obtained with the slab entirely casted in HSC.authorsversionpublishe

Flexural strengthening of flat slabs with FRP composites using EBR and EBROG methods

One of the major disadvantages of conventional fibre-reinforced polymer (FRP) strengthening techniques is the premature debonding of the FRP, leading to an underutilization of the materials. The externally bonded reinforcement on grooves (EBROG) method, which has been proven successful in postponing debonding in several structural applications, is examined in this study for the first time for realistic conditions in flat slabs. To this end, two different layouts of the strengthening solution are tested under concentric monotonic loading: one representing roof-level slab-column connections in which carbon FRP (CFRP) sheets are laid on top of the joint region (cross layout); and another one representing intermediate floors, in which the aforementioned layout is not possible due to the presence of the column (grid layout). For each layout, two FRP bonding techniques are used: conventional externally bonded reinforcement (EBR) and EBROG. Another specimen, without FRP strengthening, is used as a reference. It is shown that the EBROG technique is effective in postponing debonding for both layouts. Compared to the specimens in which EBR was used, the load capacity was increased in case of EBROG by 36% when FRP sheets were bonded on top of the joint (cross layout) and by 15% when sheets were attached outside the joint region (grid layout). Debonding strains are shown to be significantly higher in the case of EBROG compared to EBR. The experimentally observed debonding strains were compared with code provisions and predictions of models from the literature. A simple calculation method giving reasonably good results for the load capacity of the FRP-strengthened specimens is presented.authorsversionpublishe

column connections under cyclic lateral loading

For their help in the laboratory, the authors also acknowledge Rafael Sanabria Díaz, Peyman Ghaderi and Bruno Moniz. Publisher Copyright: © Fédération Internationale du Béton – International Federation for Structural Concrete.Punching shear reinforcement has already proved to be a reliable solution to improve the deformation capacity of flat slab – column connections subjected to seismic actions. Alternative approaches are becoming attractive with the development of materials such as High-Performance Fibre Reinforced Concrete (HPFRC) with better performance in tension and compression compared to conventional concrete. Motivated by the promising results obtained during an experimental campaign on hybrid HPFRC flat slabs under monotonic centred vertical loading, this paper investigates the possibility of using HPFRC to improve the behaviour of flat slabs under lateral loading (such as during earthquakes). Four reversed horizontal cyclic loading tests, under constant gravity loads, are presented. The flexural reinforcement ratio, the extent of HPFRC zone from the face of the column and the gravity load were the experimental variables considered. Results show that HPFRC can be a promising alternative to conventional punching shear reinforcement in slab column connections subjected to seismic actions, leading to increased deformation capacity. Furthermore, the results show that even a small extent of the HPFRC zone (up to 1.5 times from the face of the column) can lead to significant benefits in terms of seismic behaviour of slab – column connections, opening the possibility for an optimization of use of HPFRC.authorsversionpublishe

Behavior of flat slabs with partial use of high-performance fiber reinforced concrete under monotonic vertical loading

Funding Information: This work was financially supported by the Fundação para a Ciência e Tecnologia – Ministério da Ciência, Tecnologia e Ensino Superior through project PTDC/ECI-EST/ 30511/2017 funded by national funds (PIDDAC). EUROMODAL, Secil, Omya Comital, Sika and Dramix are gratefully acknowledged for their collaboration and supply of materials. Publisher Copyright: © 2022 Elsevier LtdReinforced concrete flat slabs are used worldwide in multi-story buildings. In these slabs, the design is often governed by punching shear and serviceability. The mitigation of these issues during design usually leads to increased raw material consumption and costs. Previous studies have shown that using Fiber Reinforced Concrete (FRC) or High-Strength Concrete (HSC) only at the vicinity of the column, while casting the rest of the slab with Normal Strength Concrete (NSC), can lead to an improved behavior under gravity loads in terms of both serviceability and ultimate capacity. Motivated by these results and the scarcity of previous tests, the present paper experimentally investigates the applicability of High-Performance Fiber Reinforced Concrete (HPFRC) as an alternative material that can be seen as an improvement over FRC and HSC, allowing a combination of ductility and strength. In addition, the HPFRC used in this paper is self-compacting, thus reducing the labor costs associated with concrete vibration. Five 150 mm thick flat slabs were tested under monotonically increasing punching load. The experimental variables were the flexural reinforcement ratio and the extent of the HPFRC zone. One of the specimens was cast only with NSC and served as a reference slab. Results show that the solution was effective for both flexural reinforcement ratios considered. Cracking load, maximum load, as well as the displacement capacity were increased significantly, even for a small extent of HPFRC (1.5 times the effective depth from the face of the column). Regarding the ultimate load capacity, it was observed an increase of 44% to 58% for the specimens with lower reinforcement ratio (0.64%) and between 15%–21% for the specimens with higher reinforcement ratio (0.96%). The results indicate that the use of HPFRC is a promising solution regarding both serviceability and ultimate limit state design of reinforced concrete flat slabs under gravity loading, with obvious advantages in material savings and labor costs.publishersversionpublishe

Seismic Performance of Strengthened Slab-Column Connections in a Full-Scale Test

Funding Information: The SlabSTRESS (Slab Structural RESponse for Seismic European Design) experimental campaign is part of the Transnational Access activities of the SERA (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe) project. This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 730900. Publisher Copyright: © 2022 The Author(s). Published with license by Taylor & Francis Group, LLC.Strengthening of flat slab-column connections to resist imposed lateral drifts is often required for older reinforced concrete structures in which the flat slabs were typically designed to resist gravity load only or have been designed for less stringent requirements. The complex stress state around the columns means that strong experimental evidence is required for the repair and strengthening techniques to be adopted with confidence in practice. Although a significant amount of research has been devoted to strengthening of slab-column connections, a series of limitations still remain. A thorough literature review revealed that only relatively thin and isolated specimens have been tested under seismic-type loading and realistic strengthening scenarios. To overcome these limitations, a full-scale two-story flat slab building specimen was tested at the European Commission’s Joint Research Centre–ELSA Laboratory in Ispra, Italy. This paper describes and analyzes the results obtained from the last of a series of phases, on repaired and strengthened internal and external slab-column connections using post-installed bolts. Compared with previous tests, the full-scale building specimen has a thicker slab (200 mm), realistic slab continuity conditions and the connections were strengthened after they suffered damage from gravity loading and previous lateral loading phases. The results show that post-installed bolts are efficient even under the described conditions (i.e. damaged and repaired specimens with realistic thickness), and punching shear failure was prevented in the strengthened connections.publishersversionepub_ahead_of_prin

Deformation capacity evaluation for flat slab seismic design

The authors acknowledge the dedicated and careful work carried out by the Associate Editor and Reviewers whose constructive criticism contributed to a very significant improvement of the quality of the paper. Authors wish to dedicate this work to the memory of their co-author Prof. Ion Radu Pascu, UTCB Bucharest, who passed away on June 10, 2021. Publisher Copyright: © 2021, The Author(s).In flat-slab frames, which are typically designed as secondary seismic structures, the shear failure of the slab around the column (punching failure) is typically the governing failure mode which limits the deformation capacity and can potentially lead to a progressive collapse of the structure. Existing rules to predict the capacity of flat slab frames to resist imposed lateral displacements without losing the capability to bear gravity loads have been derived empirically from the results of cyclic tests on thin members. These rules account explicitly only for the ratio between acting gravity loads and resistance against concentric punching shear (so-called Gravity Shear Ratio). Recent rational models to estimate the deformation capacity of flat slabs show that other parameters can play a major role and predict a significant size effect (reduced deformation for thick slabs). In this paper, a closed-form expression to predict the deformation capacity of internal slab-column connections as a function of the main parameters is derived from the same model that has been used to develop the punching shear formulae for the second generation of Eurocode 2 for concrete structures. This expression is compared to an existing database of isolated internal slab-column connections showing fine accuracy and allowing to resolve the shortcomings of existing rules. In addition, the results of a testing programme on a full-scale flat-slab frame with two stories and 12 columns are described. The differences between measured interstorey drifts and local slab rotations influencing their capacity to resist shear forces are presented and discussed. With respect to the observed deformation capacities, similar values are obtained as in the isolated specimens and the predictions are confirmed for the internal columns, but significant differences are observed between internal, edge and corner slab-column connections. The effects of punching shear reinforcement and of integrity reinforcement (required according to Eurocode 2 to prevent progressive collapse after punching) are also discussed.publishersversionpublishe