Effect of slab and transverse beam on the FRP retrofit effectiveness for existing reinforced concrete structures under seismic loading

The seismic behaviour of reinforced concrete (RC) structures is critically influenced by the complex mechanical interactions at beam-column joints. To ensure the desired hierarchy of failure is achieved when retrofitting existing structures, numerical and experimental assessments need to represent realistic structures. A review of published literature indicates that most experimental work on the seismic behaviour pre-1970′s RC beam-column connections considers sub-assemblies without slabs or transverse beams, which are unrepresentative of reality. To evaluate the effect of these elements on the failure mechanism, retrofit need and retrofit effectiveness, experiments on four full-scale beam-column joints are carried out. Two specimens with and without slab and transverse beams, are tested in their as-built and FRP strengthened configurations. As expected, the experimental results demonstrate that the progression of damage and failure mechanisms differ significantly when slabs and transverse beams are present, confirming previous numerical and experimental evidence on the strong contribution of these elements on the overall joint behaviour. Moreover, a significantly higher retrofit effectiveness is observed for the specimen without slab and transverse beam. This implies that experiments on retrofitted joints without slab and transverse beam can lead to a focus on joint shear strengthening alone as they inadequately represent the hierarchy of strengths of the framing members. They can also lead to an overestimation of retrofit effectiveness. These observations have implications when considering common simplifying assumptions made in the numerical modelling of RC moment resisting frames when assessing their seismic performance

A realistic full CFRP retrofit of RC beam-column joints compared to seismically designed specimen

The brittle collapse of reinforced concrete (RC) structures built before the introduction of detailed seismic design codes (pre- 1970’s) in recent earthquakes, has underlined the need for significant upgrades to the existing RC building stock. In particular, the observation of weak-column/strong-beam mechanisms has potentially catastrophic impacts that could be addressed by retrofit solutions. Retrofits with fibre reinforced polymers (FRP) have become increasingly popular and experimental evidence for their effectiveness can be found in the literature. The lack of tests on full-scale specimens with slabs and transverse beams in many studies may however lead to an unrealistic assessment of FRP retrofit schemes. In this study, three realistic full-scale interior beam-column joints with slab and transverse beams are tested under cyclic loading in order to propose and assess practical FRP retrofit solutions. A complete Carbon FRP (CFRP) retrofit strategy aiming to obtain a similar performance to a specimen designed to modern European design guidelines (Eurocode 8) is presented. The retrofit scheme is composed of selective strengthening and weakening components to ensure ductile failure of the specimen according to capacity design principles. Results from full-scale cyclic tests on the CFRP retrofitted specimen are compared to the behaviour of a deficient, pre-1970’s design specimen and a specimen designed to modern guidelines. The observed failure mechanisms and global lateral capacities for the Eurocode 8 and retrofitted specimen show that the CFRP retrofit is effective in improving seismic behaviour. By means of a combined selective weakening and strengthening scheme, a change in hierarchy of strengths can be achieved, which leads to an improved ductile behaviour with significant strength enhancement. The results suggest that a CFRP retrofit scheme can be devised for realistic, significantly under-designed structures in order to achieve a similar performance to modern RC structures designed to sophisticated seismic guidelines

Integrated seismic and energy retrofitting of existing buildings: A state-of-the-art review

Ageing of the building stock is an issue affecting many regions in the world. This means a large proportion of existing buildings being considered energy inefficient, with associated high energy use for heating and cooling. Through renovation, it is possible to improve their energy-efficiency, hence reducing their significant impact on the total energy household and associated greenhouse gas emissions. In seismic regions, additionally, recent earthquakes have caused significant economic losses, largely due to the vulnerability of older buildings not designed to modern standards. Addressing seismic and energy performance by separate interventions is the common approach currently taken, however to achieve better cost-effectiveness, safety and efficiency, a novel holistic approach to building renovation is an emerging topic in the scientific literature. Proposed solutions range from integrated exoskeleton solutions, over strengthening and insulation solutions for the existing building envelope or their replacement with better materials, to integrated interventions on horizontal elements like roof and floor slabs. To identify pathways to combined seismic and energy retrofitting of buildings, a state-of-the-art review of all materials and solutions investigated to date is presented. This is followed by a critical analysis of their effectiveness, invasiveness, building use disruption as well as their impact on the environment. The assessment of current combined retrofitting research highlights a great potential for their application, with a potential to provide cost-effective renovation solutions for regions with moderate to high seismic risk. Still, to-date there is a lack of experimental research in this field, a need for further work on truly integrated technologies and their validation through applications on existing large-scale buildings. Moreover, there is a need for adequate design methods, regulations and incentives that further the implementation of integrated retrofitting approaches

Experimental Comparison of Novel CFRP Retrofit Schemes for Realistic Full-Scale RC Beam-Column Joints

Existing RC moment-resisting frames (MRF) built with inadequate detailing or before the introduction of detailed seismic design codes (pre-1970s) are highly vulnerable to brittle failure mechanisms under earthquake loading. To prevent potentially catastrophic failures and consequent human and economic losses in future earthquakes, efficient and practical retrofit solutions are required for these buildings. This paper presents an experimental study focused on the development of retrofit solutions that adopt carbon fiber–reinforced polymers (CFRP) to improve the seismic performance of existing RC MRF at their beam–column connections. It is highlighted that to date, most experimental studies in this field used simplified test specimens that have ignored the presence of slabs and secondary beams at beam–column connections. This may lead to an unrealistic assessment of FRP retrofit schemes. Hence, in this study, results from six full-scale cyclic tests on typical pre-1970s interior beam–column joints with slab and transverse beams are presented. The tests are used to assess three proposed CFRP schemes composed of a combination of FRP strengthening methods and selective slab weakening. Each scheme is designed to meet a distinct retrofit objective: (1) enhancement of the lateral-load capacity, (2) enhancement of ductility, and (3) enhancement of the lateral-load capacity and ductility, as well as changing the dominant failure mode of the joint from a column hinging mechanism to one where the plasticity is mainly concentrated in the beams. A comparison of the retrofitted specimens with the behavior of a deficient specimen and a specimen designed to modern guidelines highlights the successful achievement of the respective retrofit objectives and the necessity to weaken the slab to achieve a favorable failure mechanism that will allow compliance to be achieved with current retrofit codes

A Practical Guide to the New European Bauhaus Self-assessment Method and Tool

This handbook provides a complete guide to the New European Bauhaus (NEB) self-assessment method, designed to promote the three NEB dimensions, namely sustainability, beauty, and inclusiveness, in the built environment of Europe and beyond. The handbook comes together with an online tool allowing to evaluate the performance of projects and support their improvement. The online tool is seen as the basis to establish a dialogue between all involved stakeholders, and the grounds for defining minimum performance levels within the NEB framework. Advanced targets and indices are proposed to help professionals assess all aspects of the three NEB dimensions in buildings and living spaces, promote sustainable economic and financial activities, overcome local constraints, and improve the quality of life of the European citizens, indoors and outdoors, through a built environment designed to be affordable, aesthetically appealing, healthy, comfortable, and accessible for everyone, also addressing safety, functionality under hazards, adaptation to new functions. Acknowledging the complexity of a comprehensive evaluation, and understanding the variability of metrics associated with the three NEB dimensions across different project types, scales, and geographical regions, the self-assessment method is structured hierarchically to provide feedback with three interconnected assessment levels: indicator, key performance indicator, and dimension. Specifically, the method defines three spatial scales, i.e. building, neighbourhood, and urban, and delineates two project types, i.e. newbuild and renovation. Supporting the self-assessment process, the online tool aims to facilitate the user and simplify the evaluation process while upholding the method integrity and effectiveness. This handbook offers a thorough guidance on the New European Bauhaus self-assessment method and its underlying principles. It covers assessment targets, indicators, key performance indicators, evaluation methods, and measurement units. Additionally, the handbook includes illustrative examples, empowering the interested users with the knowledge necessary to perform the evaluation effectively. The handbook primarily targets professionals engaged in both the delivery phase (design, construction, and commissioning) and the operational phase (operations and maintenance). Project managers, architects, engineers, and consultants are anticipated to play an active role in gathering and generating the information needed for the self-assessment. However, various stakeholders throughout the entire building lifecycle and supply chains are also expected to participate, benefit from, and be influenced by the assessment, including product manufacturers, main and specialist contractors, policymakers, building users and the local community members directly impacted by the project outcomes. The method is not intended to foster competition or reward high-scoring projects; rather, its purpose is to drive continuous improvement in the built environment quality and align projects with the NEB objectives. Whereas users are expected to aim at the highest performance in the self-assessment, the decision of focusing more on some performance indicators rather than others is finally left each user. To emphasise the significance of a balanced performance across all three dimensions of projects, the possibility of obtaining a global performance combining the three NEB dimension scores was intentionally excluded

Temporary techno-social gatherings? A (hacked) discussion about open practices

This paper is rooted in an experimental inquiry of issue-oriented temporary techno-social gatherings or TTGs, which are typically referred to as hackathons, workshops or pop-ups and employ rapid design and development practices to tackle technical challenges while engaging with social issues. Based on a collaboration between three digital practitioners (a producer, a researcher and a designer), qualitative and creative data was gathered across five different kinds of TTG events in London and in Tartu which were held in partnership with large institutions, including Art:Work at Tate Exchange within Tate Modern, the Mozilla Festival at Ravensbourne College and the 2017 Association of Internet Researchers conference hosted in Tartu. By analysing data using an open and discursive approach manifested in both text and visual formats, we reflect on the dynamic and generative characteristics of TTG gatherings while also arriving at our own conclusions as situated researchers and practitioners who are ourselves engaged in increasingly messy webs where new worlds of theory and practice are built

Experimental Investigation on the Seismic FRP Retrofit of Realistic Full-Scale RC Beam-Column Joints

The results of four cyclic tests on full-scale beam-column joints with typical pre-1970s deficiencies are presented. The challenges incurred by the presence of a floor slab and transverse beams in retrofitting deficient specimens are often ignored, but are here fully taken into account in the experimental set-up. A realistic repair and retrofit scheme using carbon fibre-reinforced polymer (CFRP) sheets is proposed. The scheme aims to improve the ductility of the deficient joints, while providing continuity of the flexural strengthening through the joint. The results highlight that the proposed retrofit can successfully increase the ductility of the joint by activating the beams. The presence of the slab has a significant effect on the global behaviour of the sub-assembly, which ultimately does not reach failure in the beams due to the stiff slab limiting rotation. Despite significant pre-damage, the repair scheme is very efficient, with only minor differences in terms of initial stiffness and lateral strength compared to the retrofit

Use of DIC and AE for Monitoring Effective Strain and Debonding in FRP and FRCM-Retrofitted RC Beams

Effective strain in composites as well as potential rupture and debonding of composite materials play a crucial role in predicting the strength of retrofitted reinforced concrete (RC) beams. However, only limited experimental data on these phenomena is available, mainly due to the inadequacy of traditional monitoring systems. This paper presents a comparative analysis of different instrumentation for monitoring retrofitted RC elements. In particular, the paper addresses beams retrofitted with composite materials (FRP and FRCM) and considers strain gauges (SG), fibre-optic Bragg grating (FBG) sensors, linear variable differential transformer (LVDT), digital image correlation (DIC) and acoustic emission (AE) sensors for monitoring strain, displacement, cracking and debonding. Experiments on six beams were carried out and the measured data from the monitoring devices was compared. The accuracy of DIC for strain and displacement monitoring, as well as the ability of using AE for detecting cracks and debonding, were shown to match the performance of traditional methods, with the added benefit of providing full-field and depth monitoring. This is of particular interest for composite-strengthened concrete elements in which the accurate measurements of effective strain and debonding of the composite material can lead to developing more precise design formulae. © ASCE 2016. The published version is available in the ASCE Civil Engineering Database (http://cedb.asce.org