Challenge Journal of Structural Mechanics

7-16

Authors: Seong-woo Woo, Dennis L. O’Neal

A newly designed hinge kit system (HKS) of a commercial refrigerator was subjected to a robust reliability methodology during the design phase of the system. This methodology included setting the overall parametric accelerated life test (ALT) plan of product and identifying failure mechanisms and modes in field. The ALT included a sample size equation to improve several of the HKS design parameters. Reliability of the new HKS was targeted to be 10 years over B1. Failure sites in the HKS were identified through returned products from the field. The first ALT confirmed a failure that occurred at the housing of HKS. The missing design parameters of HKS housing for the refrigerator were that it had no support ribs in the original design. The supporting structure of HKS in the refrigerator was modified based on the action plan. Cracks were identified in a second ALT that was generated in the torsional shaft. Due to it having squared off corners, the HKS torsional shaft did not have not enough strength to withstand repetitive stresses. The shaft was modified as a consequence of the ALTs. The reliability of redesigned HKS is now guaranteed as B1 10 years. The design methods - load analysis and three ALTs were very effective in identifying the missing design parameters during the design phase. The robust design method presented in this paper might be applicable to the other mechanical systems.

25-32

Authors: Paata Rekvava, Ketevan Mdivani

The utilization of time histories of earthquake ground motion has grown considerably in the field of earthquake engineering. It is very unlikely, however, that recordings of earthquake ground motion will be available for all sites and conditions of interest. Hence, there is a need for efficient methods for the simulation of strong ground motion for a given region. Due to lack of the real strong ground motion records the objective of this research is to develop a methodology for rapid generation of horizontal and vertical components of earthquake ground motion at any site for Tbilisi city. The model developed in this study provides simulation of ground motion over a wide range of magnitudes and distances at 8 earthquake sources zones of Tbilisi region (within 50 km). The research includes three main topics: (i) the stochastic simulation of earthquake ground motion at a given site of the city of Tbilisi; (ii) the estimation of acceleration time histories at a given site using the direct method of engineering seismology considering soil conditions based on the theory of the reflected waves and (iii) calculation of horizontal and vertical acceleration elastic response spectra for main sites of Tbilisi territory. The simulation procedure typically consists of multiplying deterministic modulating function with a stationary process of known power spectral density. The obtained results in the terms of normalized elastic response spectra can be widely applied in the practice of earthquake engineering in Georgia.

41-53

Authors: Tuğba Türker, Yusuf Bayrak

North Anatolian Fault (NAF) is one from the most important strike-slip fault zones in the world and located among regions in the highest seismic activity. The NAFZ observed very large earthquakes from the past to present. The aim of this study; the important parameters of Gutenberg-Richter relationship (a and b values) estimated and this parameters taking into account, earthquakes were examined in the between years 1900-2015 for 10 different seismic source regions in the NAFZ. After that estimated occurrence probabilities and return periods of occurring earthquakes in fault zone in the next years, and is being assessed with Poisson method the earthquake hazard of the NAFZ. The 10 different seismic source regions are determined the relationships between the cumulative number-magnitude which estimated a and b parameters with the equation of LogN=a-bM in the Gutenberg-Richter. A homogenous earthquake catalog for MS magnitude which is equal or larger than 4.0 is used for the time period between 1900 and 2015. The database of catalog used in the study has been created from International Seismological Center (ISC) and Boğazici University Kandilli observation and earthquake research institute (KOERI). The earthquake data were obtained until from 1900 to 1974 from KOERI and ISC until from 1974 to 2015 from KOERI. The probabilities of the earthquake occurring are estimated for the next 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 years in the 10 different seismic source regions. The highest earthquake occur probabilities in 10 different seismic source regions in the next years estimated that the region Tokat-Erzincan (Region 9) 99% with an earthquake occur probability for magnitude 6.5 which the return period 24.7 year, 92% with an earthquake occur probability for magnitude 7 which the return period 39.1 year, 80% with an earthquake occur probability for magnitude 7.5 which the return period 62.1 year, 64% with an earthquake occur probability for magnitude 8 which the return period 98.5 year. For the Marmara Region (Region 2) in the next 100 year estimated that 89% with an earthquake occur probability for magnitude 6 which the return period 44.9 year, 45% with an earthquake occur probability for magnitude 6.5 which the return period 87 year, 45% with an earthquake occur probability for magnitude 7 which the return period 168.6 year.

61-70

Authors: Atila Kumbasaroğlu, Ahmet Budak

In this study, a series of experimental study was conducted to investigate the effect of anchor bars on steel frame systems where the connections were provided by anchor bars between frame and infilled walls. Seven one over four scaled specimens having one story and one bay of frames were tested. Experimental study was carried out by damage-controlled and incrementally applied load up to loading cracks. The test results relieved that with the help of using anchor bars the capacity of energy absorption with initial stiffness were increased. It has been found that the frames without using anchor bars failure at the loading edge, the crushing behavior of infilled walls and separations at free edges were occurred. These observed failure behaviors replies with tensile cracking for the frames having anchor bars. There for it should be underlined that anchor bars have a significant effect on improving the behavior of the frames.

7-13

Authors: Stergios A. Mitoulis

This paper summarises the ongoing research on the seismic design of isolated and integral bridges at the University of Surrey. The first part of the paper focuses on the tensile stresses of elastomeric bearings that might be developed under seismic excitations, due to the rotations of the pier cap. The problem is described analytically and a multi-level performance criterion is proposed to limit the tensile stresses on the isolators. The second part of the paper sheds light on the response of integral bridges and the interaction with the backfill soil. A method for the estimation of the equivalent damping ratio of short-span integral bridges is presented to enable the seismic design of short period bridges based on Eurocode 8-2. For long-span integral bridges, a novel isolation scheme is proposed for the abutment. The isolator is a compressible inclusion comprises tyre derived aggregates (TDA) and is placed between the abutment and a mechanically stabilised backfill. The analysis of the isolated abutment showed that the compressible inclusion achieves to decouple the response of the bridge from the backfill. The analyses showed that both the pressures on the abutment and the settlements of the backfill soil were significantly reduced under the thermal and the seismic movements of the abutment. Thus, the proposed decoupling of the bridge from the abutment enables designs of long-span integral bridges based on ductility and reduces both construction and maintenance costs.

25-31

Authors: Robert Korol, Paul Heerema, Ken Sivakumaran

Although the events of that tragic day happened 14 years ago, there remain nagging questions of why the 47 storey WTC 7 steel framed structure collapsed, when it was NOT hit by an airplane. We will review the official rationale of how the collapse events started, and why, in our opinion, the explanation is judged to be wrong. Then, we will proceed with another scenario that says “Okay – let’s assume that the two critical storeys did sustain extremely hot fires, so much so that 2/3rds of their columns totally lost axial resistance capability”. We then proceed to employ Newton’s laws to inquire whether there was sufficient gravitational potential energy due to live and dead loadings in upper and lower floors to overcome the resistance offered by the remaining columns, together with floor slabs known to have been pulverized to reduced particle sizes by surface to surface crushing. Our conclusion suggests that Newton’s laws of motion and energy conservation considerations would have had to have been violated to explain that building’s total collapse within a debris pile several storeys high.

38-50

Authors: Shota Urushadze, Miroš Pirner

The authors have noticed the newest observations and few analysis of excitation mechanism. Therefore they prepared the series of vertical and lateral forces measurements due to steps of walking, running persons on horizontal plane, on inclined plane and on stairway. They suppose that the import knowledge of the forces frequencies of step or strides for different walking velocities is the most important for the further analysis and analysis of the mechanisms. The time histories of lateral forces of a pedestrian were registered and statistical analyzed: the authors received the lateral force dependence on the walking velocity, on stride length an on the weight of pedestrian. The new research step is focused on lateral horizontal forces.

60-68

Authors: Amaia Martinez, Carlos E. Ventura

The purpose of this paper is to compare the response of a ten story concrete building in San Jose, California, under three different earthquakes. The strong-motion records of the instrumented building obtained during the 1984 Morgan Hill earthquake were used to calibrate a finite element model. Soil-structure interaction was included in the model by adding some translational springs to the foundation. The same model was subjected to 1986 Mount Lewis and 1989 Loma Prieta earthquakes. While for the first case a good match between the recorded data and analytical results was obtained, for the second one the match was not as good as expected. A modal identification analysis of the building was conducted for the three ground motions using both just output operational modal analysis (OMA) and input-output experimental modal analysis (EMA). It was demonstrated that for Loma Prieta, which presents higher amplitude shaking than the other two ground motions, the fundamental period for the transversal mode of the structure was higher than that obtained using the other two earthquakes. Consequently, the springs of the finite element model needed to be updated for Loma Prieta in order to capture the more flexible response of the building. After this adjustment, there was a good match between the recorded motions and analytical results. This study proves that the effects of soil-structure interaction becomes very important when a building is subjected to high levels of shaking. In some cases, a single model of a building with concrete shear walls may not be suitable to predict properly the behavior of the building under different ground motions.