Nicholas Kyriakides

Full-Scale Shaking Table Tests on a Substandard RC Building Repaired and Strengthened with Post-Tensioned Metal Straps

The effectiveness of a novel Post-Tensioned Metal Strapping (PTMS) technique at enhancing the seismic behavior of a substandard RC building was investigated through full-scale, shake-table tests during the EU-funded project BANDIT. The building had inadequate reinforcement detailing in columns and joints to replicate old construction practices. After the bare building was initially damaged significantly, it was repaired and strengthened with PTMS to perform additional seismic tests. The PTMS technique improved considerably the seismic performance of the tested building. While the bare building experienced critical damage at an earthquake of PGA = 0.15 g, the PTMS-strengthened building sustained a PGA = 0.35 g earthquake without compromising stability.

Pseudo-Dynamic Tests on a Full-Scale Four-Storey Reinforced Concrete Frame Seismically Retrofitted with Reinforced Concrete Infilling

Abstract The effectiveness of seismic retrofitting of multi-storey multi-bay reinforced concrete (RC)-frame buildings by converting selected bays into new walls through infilling with RC was studied experimentally at the ELSA facility of the Joint Research Centre in Ispra (Italy). A full-scale model was tested with the pseudo-dynamic (PsD) method and consisted of two four-storey (12 m tall) three-bay (8,5 m long) parallel frames linked through 0,15 m slabs with the central bay (2,5 m) infilled with an RC wall. The frames were designed and detailed for gravity loads only and were typical of similar frames built in Cyprus in the 1970s. Different connection details and reinforcement percentages for the two infilled frames were used in order to study their effects in determining structural response. The results of the pseudo-dynamic and cyclic tests performed on the specimen are presented, and conclusions are drawn.

Seismic retrofitting and health monitoring of school buildings of Cyprus

The vulnerability of existing buildings to seismic forces and their retrofitting is an international problem. The majority of structures in seismic-prone areas worldwide are structures that have been designed either without the consideration of seismic forces, or with previous codes of practice specifying lower levels of seismic forces. In Cyprus, after the three earthquakes that occurred in 1995, 1996, and 1999, the Cyprus State, acting in a pioneering way internationally, has decided the seismic retrofitting of all school buildings, taking into account the sensitivity of the society towards these structures, which house the future generation of the society. In this paper the overall assessment methodology is presented, along with details of the over 10 year ongoing retrofitting program of the school buildings of Cyprus, with emphasis on the description of the program and the development of a wireless monitoring system. In addition, mathematical models of selected school buildings are presented and comparison is made with in-situ measurement.

Seismic fragility assessment of existing sub-standard low strength reinforced concrete structures

An analytical seismic fragility assessment framework is presented for the existing low strength reinforced concrete structures more common in the building stock of the developing countries. For realistic modelling of such substandard structures, low strength concrete stress-strain and bond-slip capacity models are included in calibrating material models. Key capacity parameters are generated stochastically to produce building population and cyclic pushover analysis is carried out to capture inelastic behaviour. Secant period values are evaluated corresponding to each displacement step on the capacity curves and used as seismic demand. A modified capacity demand diagram method is adopted for the degrading structures, which is further used to evaluate peak ground acceleration from back analysis considering each point on the capacity curve as performance point. For developing fragility curves, the mean values of peak ground acceleration are evaluated corresponding to each performance point on the series of capacity curves. A suitable probability distribution function is adopted for the secant period scatter at different mean peak ground acceleration values and probability of exceedance of limit states is evaluated. A suitable regression function is used for developing fragility curves and regression coefficients are proposed for different confidence levels. Fragility curves are presented for a low rise pre-seismic code reinforced concrete structure typical of developing countries.

Vulnerability assessment and feasibility analysis of seismic strengthening of school buildings

Abstract The majority of structures in seismic-prone areas worldwide are structures that have been designed either without seismic design considerations, or using codes of practice that are seriously inadequate in the light of current seismic design principles. In Cyprus, after a series of earthquakes that occurred between 1995 and 1999, it was decided to carry out an unprecedented internationally seismic retrofitting of all school buildings, taking into account the sensitivity of the society towards these structures. In this paper representative school buildings are analysed in both their pristine condition and after applying retrofitting schemes typical of those implemented in the aforementioned large-scale strengthening programme. Non-linear analysis is conducted on calibrated analytical models of the selected buildings and fragility curves are derived for typical reinforced concrete and unreinforced masonry structures. These curves are then used to carry out a feasibility study, including both benefit-cost and life-cycle analysis, and evaluate the effectiveness of the strengthening programme.

RC infilling of existing RC structures for seismic retrofitting

The effectiveness of seismic retrofitting of multi-storey multi-bay RC-frame buildings by converting selected bays into new walls through infilling with reinforced concrete (RC) was studied experimentally at the ELSA facility of the Joint Research Centre in Ispra (Italy). A full-scale structure was tested with the pseudo-dynamic method. It consisted of 2 four-storey (12 m tall) three-bay (8.5 m long) parallel frames linked through 0.15 m slabs. The central bay (2.5 m) of each frame is infilled with a RC wall. The frames were designed and detailed for gravity loads only and are typical of similar frames built in Cyprus in the 1970s. Different connection details and reinforcement percentages for the two infilled frames were used in order to study their effects in determining structural response. The results of the pseudo-dynamic and cyclic tests performed on the specimen are presented, and conclusions are drawn.

Evaluation of Seismic Demand for Substandard Reinforced Concrete Structures

Background: Reinforced Concrete (RC) buildings with no seismic design exhibit degrading behaviour under severe seismic loading due to non-ductile brittle failure modes. The seismic performance of such substandard structures can be predicted using existing capacity demand diagram methods through the idealization of the non-linear capacity curve of the degrading system, and its comparison with a reduced earthquake demand spectrum. Objective: Modern non-linear static methods for derivation of capacity curves incorporate idealization assumptions that are too simplistic and do not apply for sub-standard buildings. The conventional idealisation procedures cannot maintain the true strength degradation behaviour of such structures in the post-peak part, and thus may lead to significant errors in seismic performance prediction especially in the cases of brittle failure modes dominating the response. Method: In order to increase the accuracy of the prediction, an alternative idealisation procedure using equivalent elastic perfectly plastic systems is proposed herein that can be used in conjunction with any capacity demand diagram method. Results: Moreover, the performance of this improved equivalent linearization procedure in predicting the response of an RC frame is assessed herein. Conclusion: This improved idealization procedure has been proven to reduce the error in the seismic performance prediction as compared to seismic shaking table test results [1] and will be further investigated probabilistically herein.

Applications of thermal imaging camera for assessing structural integrity

The ongoing degradation of structures is associated with expensive maintenance and the resulting decline in safety, force the engineer to search for structural health monitoring tools that will be fast, effective, cover large areas and cost as minimum as possible. In this context the thermal imaging cameras are an ideal monitoring tool; with the radical development of higher resolution thermal imaging, the decreasing cost of the camera and its portable size makes this technology promising to accomplish the requirements of modern structural monitoring. Thermal imaging camera uses algorithms to interpret visual displays of the amount of infrared energy emitted, transmitted and reflected by an object and form images that are invisible to the human eye. Therefore, the thermal imaging technology can be used as a tool to help the engineer gain better insight and viable information and thus enabling the structure to retain/sustain its function, form and strength within acceptable limits under operational loading. This paper presents applications of this technology for assessing the integrity of structures along with possible trends and gains on different areas of structural integrity, such as the detection of corrosion in steel rebars embedded in RC structures and the chloride contents on concrete surface.

Framework for an integrated system for enhancing the energy efficiency and structural performance of buildings

The building stock should be in operational and reliable state in order to ensure primarily the safety of the users. In addition to safety, nowadays the comfort of the users is of prime importance. To satisfy the required comfort levels the user should consume energy, in the form of heating, cooling etc. Therefore this ongoing trend to satisfy these conditions, results in buildings which are safer, more economic to operate and more sustainable. Taking into account economic, technical, durability and environmental factors there is the need for a holistic approach for the optimum performance of buildings for structural integrity and energy efficiency. Current practice evolves around building solutions that isolate each deficiency and proposes solutions to enhance each of the two separately. In the last few years, from a sustainability perspective, emphasis is placed on developing an integrated system for buildings that will improve simultaneously both the structural integrity and the energy performance and should be preferred over individual actions. This study investigates independent building and/or retrofit actions applied for structural strengthening and energy performance improvements that have the potential to be combined into an integrated system to enhance the overall performance of buildings. Such multidisciplinary approach will ensure that new and existing buildings satisfy both structural safety and energy efficiency targets in a more economic and effective manner. Furthermore, as first step in this direction, an experimental test program was conducted in the laboratory to examine the benefit of applying thermal insulation in the form of polystyrene on the durability context by reducing the building’s material deterioration due to environmental effects.

DYNAMIC RESPONSE OF A GOTHIC CATHEDRAL IN CYPRUS

Within the scope of this study, dynamic response of the St. Nicholas Cathedral in Cyprus that dates back to the 13th century was assessed based on obtained earthquake records. This structure resembles to the Rheims Cathedral of France with a nave of seven bays ending in a polygonal apse, together with flanking aisles ending in apsidal chapels of similar shape. According to historical records, it sustained heavy earthquake damage twice to its roof structure and flying buttresses. The main construction material used at this structure is calcarenite. Back in 2011, a strong-motion network was installed at the cathedral, which recorded a series of small to moderate magnitude events since then. This strong motion network consisting of 10 tri-axial accelerometers is the only active structural health monitoring system in Cyprus. In this article, the time-domain and frequency-domain analysis of this data is presented.