Papers by Keyword: Earthquake

Abstract: The structures are prone to dynamic loads such as earthquake as they often generate uncomfortable movement into existing structures. In order to reduce extreme vibration generated by dynamic or operational loads passive, active or hybrid controlling devices are used. And the advantages of passive systems are well accepted due to their inexpensiveness and simplicity. This study investigates the performance of a newly developed uniaxial tuned mass damper (TMD). The novelty of the developed device is that the properties of the damper are adjustable based on the structural requirements. And most importantly, another key design criterion is to make a low-cost affordable device. To do this end, a toy two degree of freedom (2-DOF) system is considered and the experiments are conducted. The experimental tests and numerical simulations are carried out on the structure without and with TMD along with extra masses of 25 kg, 30 kg and 35 kg on the floors to observe the effect of floor mass changes. The scaled El Centro 1940 earthquake data is used as input excitation. In order to determine the optimal performance of the damper, it is tuned to modal mass of 0% (i.e., without TMD), 5%, 7.5%, 10%, 12.5%, and 17.5%. The experimental results have shown that the structure without TMD has pronounced vibration (i.e., displacement) as compared to the structure with TMD. As the percentage of modal mass increases, the vibration of the structure decreases. It is observed that up to 12.5% of modal mass for both 20 and 25 sec excitation duration could be the optimum amount that minimizes the vibration of the structure. The overall performance of this device is capable of reducing vibration in a reasonable manner and has the possibility to use it for the real engineering application.

Abstract: Evaluating the integrity of a structure consists in proving its ability to realize its mechanical functions for all modes of loading, normal or accidental, and throughout its lifetime. In the context of nuclear safety, the most important structures consider the presence of a degradation grouping several aspects, such as cracks. In this context, the fracture mechanics provide the tools needed to analyze cracked components. Its purpose is to establish break criteria for judging loading margins in normal or accidental operating conditions. The seismic load is one of the dominant loads for the failure assessment of the pipes. Its probabilistic dispersion, however, was not taken into account in the past probabilistic fracture mechanics analysis. The objective of this paper is to simulate and analyze the effect of abnormal stress on the reliability of tow pipe sizes. As result the seismic stress has more effect on the break probability, but not for the leak probability. In the case without a seismic load, the break probability is mainly dominated by an initial crack size. The earthquake has much effect on the break probability for the large diameter pipe, not for the small diameter pipe. In the large diameter pipe, the break probability increases gradually with the time. The leak probability of both pipe sizes is not affected by the seismic curve.

Abstract: Realization of first-aid devices for the safety of heavily damaged structures of the Cultural Heritage assets is one of the main problems in the post-earthquake emergency phase. However, the adopted solutions, characterized by the utmost urgency, often appear uneven, ineffective and expensive. Six years after the earthquake in Emilia Romagna Region, which damaged numerous historical buildings, above all churches, it seems worthwhile to reflect on the management of the post-earthquake emergency and reconstruction interventions. As a matter of fact, in 2012, many Public Institutions were unprepared to deal with such an event: the lack of an appropriate knowledge about how to intervene in such conditions has led to solutions that are unnecessarily expensive, technically ineffective and, sometimes, even harmful for the building itself. Frequently, the strengthening devices had to be entirely redesigned during the subsequent phase of definitive intervention, entailing additional costs for the removal of those realized in the emergency phase. The cases in which the provisional devices have been designed in preparation for the final strengthening, sometimes even becoming definitive themselves, are rare. Therefore, this experience has raised some reflections concerning the functionality of the temporary safety measures. It has been noticed that an appropriate design of the provisional devices is fundamental in order to avoid interventions that could compromise the value of the architectural asset, to allow the knowledge of the structure for designing the definitive strengthening and to consider the permanent implications of such safety measures. This note presents some case-studies related to strengthening actions following the 2012 earthquake in Emilia, aiming to identify possible solutions for implementing the first-aid interventions in an integrated way with the subsequent strengthening phase in order to significantly reduce economic, material and time costs.

Abstract: Bridges are commonly used lifelines; they play an important role in the economic activity of a city or a region and their role can be crucial in a case of a seismic event since they allow the arrival of the first aid. Reinforced concrete (RC) bridges are worldwide used type view their durability, flexibility and economical cost. In fact, their behavior under seismic loading was the aim of various studies. In the present study the effect of two structural parameters i.e. the height and the type of piers of reinforced concrete bridges on seismic response is investigated. For that reason, different multi-span continuous girder bridges models with various geometrical parameters are considered. Then, non-linear dynamic analyses are performed based on two types of piers which are: multiple columns bent and wall piers with varying heights. In this approach, a serie of 40 ground motions records varying from weak to strong events selected from Building Research Institute (BRI) strong motion database are used including uncertainty in the soil and seismic characteristics. Modelling results put most emphasis on the modal periods and responses of the top pier displacements, they show the influence of the considered parameters on the behavior of such structures and their impact on the strength of reinforced concrete bridges.

Abstract: Numerous existing steel framed buildings located in earthquake prone regions world-wide were designed without seismic provisions. Slender beam-columns, as well as non-ductile beam-to-column connections have been employed for multi-storey moment-resisting frames (MRFs) built before the 80’s. Thus, widespread damage due to brittle failure has been commonly observed in the past earthquakes for steel MRFs. A recent post-earthquake survey carried out in the aftermath of the 2016-2017 Central Italy seismic swarm has pointed out that steel structures may survive the shaking caused by several main-shocks and strong aftershocks without collapsing. Inevitably, significant lateral deformations are experienced, and, in turn, non-structural components are severely damaged thus inhibiting the use of the steel building structures. The present papers illustrates the outcomes of a recent preliminary numerical study carried out for the case of a steel MRF building located in Amatrice, Central Italy, which experienced a series of ground motion excitations suffering significant damage to the masonry infills without collapsing. A refined numerical model of the sample structure has been developed on the basis of the data collected on site. Given the lack of design drawings, the structure has been re-designed in compliance with the Italian regulations imposed at the time of construction employing the allowable stress method. The earthquake performance of the case study MRF has been then investigated through advanced nonlinear dynamic analyses and its structural performance has been evaluated according to Eurocode 8-Part 3 for existing buildings. The reliability of the codified approaches has been evaluated and possible improvements emphasized.

Abstract: The Sliding Hinge Joint with Asymmetric Friction Connectors (SHJ), to give its full name, is a semi-rigid moment resisting joint used between the beams and columns of a moment-resisting steel frame and also at the column base between the column and the ground. It’s performance is intended to be as follows: 1) On completion of construction, rigid under serviceability limit state conditions, 2) During a severe earthquake, allowing controlled rotation between the column and the beam or foundation on designated friction sliding planes within the connection, then 3) Returning to its rigid in-service condition at the end of the severe shaking with the building returning to its pre-earthquake position (self-centering). During its development and proof of concept through large scale testing, the initial results showed that the SHJ as originally designed and detailed performs 1) and 2) very well, but the bolts in the friction sliding planes loose much of their original installed bolt tension during significant sliding, lowering the level at which rotation within the joint will occur post severe earthquake. A concerted research programme of component testing, analytical model development and numerical modelling in recent years has developed solutions to the bolt tension loss issue as well as enhanced the joint’s performance to deliver dependable self-centering capability for the building. This work marks the final steps towards developing an optimum low damage seismic-resisting steel moment frame system. This paper presents key findings from the research work and general recommendations for the optimum performing sliding hinge joint.

Abstract: First the Canterbury earthquake series of 2010/2012 and then the Kaikoura Earthquake of 2016 have significantly impacted the building stock in central and southern New Zealand, subjecting a wide range of buildings and building components to earthquake shaking ranging from moderate to severe. The economic and social costs of these earthquakes have been severe, but the lessons learned on how buildings and building systems designed and detailed to New Zealand provisions have performed have been invaluable. We have learned more about this from these earthquakes then from the many reconnaissance trips undertaken to overseas earthquakes over the 50 years of the New Zealand Society for Earthquake Engineering. This paper focusses on the performance of steel framed buildings in two major New Zealand cities, Christchurch and Wellington, with greatest emphasis on multi-storey buildings, but also covering light steel framed housing. It addresses such issues as the magnitude and structural impact of the earthquake series, how the various systems performed against the design expectations and briefly covers some of the research underway to quantify where there were differences between the observed performance and the expected performance.

Abstract: With increasing demands in high-rise constructions worldwide, developing a thinner steel floor system is becoming a crucial criterion in maximizing the useable and saleable spaces within a high-rise construction. This research aims to overcome the past drawbacks and develop an innovative and economical steel floor system that can be modularized and used within a modular construction. The proposed modular steel floor system can be fabricated offsite, shipped and assembled on site. This saves the construction time and fabrication cost. In this paper, the specially designed modular floor system was optimized for both gravity and lateral loads. The seismic performances of the proposed floor system are used in a 3-story prototype building. The results show that the proposed system is highly efficient in transferring the gravity and lateral loads which can be used effectively and efficiently for modular constructions worldwide.

Abstract: Buckling Restrained Braces (BRB’s) have become common in seismic frames in earthquake areas. If a BRB performs as desired the steel core may yield but it is not easy to know the degree of yielding, or how much of the BRB earthquake life has been used up. To determine whether such a brace should remain as is, or whether it needs to be replaced, an inexpensive and simple measuring device that reports the deformations undergone is required. This paper discusses a study undertaken to develop such a device. Firstly, a literature study was undertaken and candidate devices were selected. Using Subjective Quantitative Analysis (SQA) and specific performance objectives the most appropriate of these was chosen. This device was then constructed and tested in a controlled environment. This mechanical device performed well through various stimulated earthquake cycles and events, is cheap, simple to install, and small. It provides cumulative and maximum displacement estimations and will be beneficial to the industry in post-event decision making.

Abstract: Timisoara is a growing city in the western part of Romania, in a seismic area, with a lot of masonry buildings with historical and cultural value, with interesting structural elements such as vaults, arches, slabs, walls, that were affected by earthquakes, subsidence of foundations, negative human actions or lack of interventions. Masonry historical structures in Banat seismic area present particular failure mechanisms, so there is a need for new, modern, fast, easy-to-apply and reversible consolidation methods. With this type of methods is possible to assure the local and global resistance, ductility, stability and rigidity for historical buildings. This article shows the consolidation methods that were applied on the buildings Sf. Gheorghe 3 and 4, in the historical centre of Timisoara, on masonry structures with historical value. The solutions that were applied are using new, innovative fibre-reinforced composite materials, in order to repair the existing damages and prevent further ones. The consolidation solutions with these new composite materials reduce the buildings vulnerability and present the advantage of being fast and easy to be executed.