Techno Press
Tp_Editing System.E (TES.E)
Login Search
You logged in as

sem
 
CONTENTS
Volume 82, Number 5, June10 2022
 


Abstract
The retrofit of existing structures in high seismic zones is a crucial issue in the earthquake engineering field. The interest of the research community is particularly high for the structures that do not respect current seismic codes and present structural deficiencies such as poor detailing and lack of capacity design provisions. A reinforced concrete (RC) school building is used as case study to show the influence of different knowledge levels on the seismic retrofitting cost assessment. The safety assessment of the case study building highlights deficiencies under both vertical and seismic loads. By considering all the possible knowledge levels defined by the Italian such as by the European codes in order to derive the mechanical properties of the school building constitutive materials, the retrofit operations are designed to achieve different seismic safety thresholds. The retrofit structural costs are calculated and summed up to the costs for in-situ in tests. The paper shows how for the case study building the major costs spent for a large number of in-situ tests allows to save a consistent amount of money for retrofit operations. The hypothesis of demolition and reconstruction of the building is also compared in terms of costs with all the analyzed retrofit options.

Key Words
in-situ tests; knowledge levels; RC jacketing; retrofit costs; safety index; seismic retrofit; steel jacketing

Address
Andrea Miano, Giovanni Chiumiento, Antonio Formisano and Andrea Prota: Department of Structures for Engineering and Architecture, University of Naples Federico II, Via Claudio, 21, Napoli, 80125, Italy

Abstract
As a vital component of power grids, long-span transmission tower-line systems are vulnerable to wind load excitation due to their high flexibility and low structural damping. Therefore, it is essential to reduce wind-induced responses of tower-line coupling systems to ensure their safe and reliable operation. To this end, a shape memory alloy-bidirectional tuned mass damper (SMA-BTMD) is proposed in this study to reduce wind-induced vibrations of long-span transmission tower-line systems. A 1220 m Songhua River long-span transmission system is selected as the primary structure and modeled using ANSYS software. The vibration suppression performance of an optimized SMA-BTMD attached to the transmission tower is evaluated and compared with the effects of a conventional bidirectional tuned mass damper. Furthermore, the impacts of frequency ratios and SMA composition on the vibration reduction performance of the SMA-BTMD are evaluated. The results show that the SMA-BTMD provides superior vibration control of the long-span transmission tower-line system. In addition, changes in frequency ratios and SMA composition have a substantial impact on the vibration suppression effects of the SMABTMD. This research can provide a reference for the practical engineering application of the SMA-BTMD developed in this study.

Key Words
bidirectional tuned mass damper; long-span transmission tower-line system; shape memory alloy; vibration control; wind excitation

Address
Li Tian, Jingyu Luo, Mengyao Zhou, Wenzhe Bi and Yuping Liu: School of Civil Engineering, Shandong University, Jinan 250061, Shandong, China

Abstract
Behavior of concrete elements under the effect of high-speed projectiles has gain increasing interest recently. It's necessary to understand how far the concrete can absorb the effect of bullets in order to save the occupants when design security and military infrastructures. This study presents a total of 18 concrete slabs casted and tested under reinforcement ratios, 0%, 0.35% and 0.7%. Parameters interested were slab thickness, (50 mm, 100 mm, and 150 mm) and type of weapon. All specimens tested to investigate their response under the effect of attacking by two common types of weapon. In general, it was found that projectile penetration was controlled by their thickness regardless the steel reinforcement ratio. However, the steel reinforcement controls the damage.

Key Words
bullet; concrete plate; crater; high-speed projectile; penetration

Address
Abdalla S. Tais, Omer F. Ibraheem and Saad M. Raoof: Department of Civil Engineering, University of Tikrit, Tikrit, Iraq

Abstract
Prestressed composite steel-concrete beams are still a technology restricted to repair sites of large-scale structures and spans. One of the reasons for that is the absence of standard frameworks and publications regarding their design and implementation. In addition, the primary normative codes do not address this subject directly, which might be related to a scarcity of papers indicating methods of design that would align the two technics, composite beams and external prestressing. In this context, this paper proposes methods to analyze the sizing of prestressed composite beams submitted to pre-tension and post-tension with a straight or polynomial layout cable. This inquiry inspected a hundred and twenty models of prestressed composite beams according to its prestressing technology and the eccentricity and value of the prestressing force. The evaluation also included the ratio between span and height of the steel profile, thickness and typology of the concrete slab, and layout of the prestressing cables. As for the results, it was observed that the eccentricity of the prestressing force doesn't significantly influence the bending resistance. In prestressed composite beams subjected to a sagging moment, the ratio L/d can reach 35 and 30 for steel-concrete composite slabs and solid concrete slabs, respectively. Considering the negative bending moment resistance, the value of the L/d ratio must be less than or equal to 25, regardless of the type of slab. When it comes to the value of the prestressing force, a variation greater than 10% causes a 2.6% increase in the positive bending moment resistance and a 4% decrease in the negative bending moment resistance. The pre-tensioned composite beams showed a superior response to flexural-compression and excessive compression limit states than the post-tensioned ones.

Key Words
composite steel-concrete beams; computer program; design methodologies; external prestressing; pretension and pos-tension

Address
Thiago T. Turini and Adenilcia F.G. Calenzani: Department of Civil Engineering, Federal University of Espirito Santo, Av. Fernando Ferrari, 514, Goiabeiras, Vitória, Espírito Santo, Brazil

Abstract
Energy-dissipative rocking (EDR) columns are a class of seismic mitigation device capable of dissipating seismic energy and preventing weak-story failure of moment resisting frames (MRFs). An EDR consists of two hinge-supported steel columns interconnected by steel dampers along its height. Under earthquakes, the input seismic energy can be dissipated by plastic energy of the steel dampers in the EDR column. However, the unrecoverable plastic deformation of steel dampers generally results in residual drifts in the structural system. This paper presents a proof-of-concept study on an innovative device, namely self-centring energy-dissipative rocking (SC-EDR) column, aiming at enabling self-centring capability of the EDR column by installing a set of shape memory alloy (SMA) tension braces. The working mechanism of the SC-EDR column is presented in detail, and the feasibility of the new device is carefully examined via experimental and numerical studies considering the parameters of the SMA bar diameter and the steel damper plate thickness. The seismic responses including load carrying capacities, stress distributions, base rocking behaviour, source of residual deformation, and energy dissipation are discussed in detail. A rational combination of the steel damper and the SMA tension braces can achieve excellent energy dissipation and self-centring performance.

Key Words
energy dissipation; self-centring; shape memory alloy (SMA); steel rocking column; tension brace

Address
Yan-Wen Li: Department of Architecture and Architectural Engineering, Kyoto University, Kyoto, Japan; Department of Building & Real Estate, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China
Michael C.H. Yam: Department of Building & Real Estate, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China
Ping Zhang: Department of Building & Real Estate, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China
Ke Ke: Key Laboratory of New Technology for Construction of Cities in Mountain Area, School of Civil Engineering, Chongqing University, Chongqing, China
Yan-Bo Wang: College of Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
This study deals with the spinning impact on flap-wise vibration characteristics of nonlocal functionally graded (FG) cylindrical beam based on the Hyperbolic shear deformation beam theory. The nonlocal strain gradient theory is used to investigate the small-scale impact on the nonlocal motion equation as well as corresponding nonlocal boundary conditions. Based on the mathematical simulation and according to the Hamilton principle, the computerized modeling of a rotating functionally graded nanotube is generated, and then, via a numerical approach, the obtained mathematical equations are solved. The calculated outcomes are helpful to the production of Nano-electro-mechanical-systems (NEMS) by investigating some designed parameters such as rotating speed, hub radius, length-scale parameters, volume fraction parameters, etc.

Key Words
Hyperbolic shear deformation beam theory; nonlocal strain gradient theory; numerical analysis; rotating nanobeam

Address
Lingao Zhou: School of Electronic Engineering, Changzhou College of Information Technology, Changzhou 213164, Jiangsu, China

Abstract
In this paper a novel mathematical model and its analytical solution of global buckling behaviour of slender elastic concrete-filled double-skin tubular (CFDST) columns with finite compliance between the steel tubes and a sandwiched concrete core is derived for the first time. The model is capable of investigating the influence of various basic parameters on critical buckling loads of CFDST columns. It is shown that the elastic buckling load of circular and slender CFDST columns is independent on longitudinal contact stiffness, but, on the other hand, it can be considerably dependent on circumferential contact stiffness. The increasing of the circumferential contact stiffness increases the critical buckling load. Furthermore, it is shown that analytical results can agree well with the experimental and numerical results if the calibrated values of circumferential contact stiffness are used in the calculations. Moreover, it is shown that the contact between the steel tubes and a sandwiched concrete core of tested large-scale CFDST columns used in the comparison is relatively weak. Finally, the proposed analytical results can be used as a benchmark solution.

Key Words
buckling; CFDST; column; contact; double-skin

Address
Bojan Čas: Faculty of Civil and Geodetic Engineering, University of Ljubljana, Jamova 2, 1000 Ljubljana, Slovenia
Simon Schnabl: Faculty of Civil and Geodetic Engineering, University of Ljubljana, Jamova 2, 1000 Ljubljana, Slovenia; Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, 1000 Ljubljana, Slovenia

Abstract
While the lateral confinement provided by an FRP jacket to a concrete column is passive in nature, confinement is activated when the concrete expands due to additional compression stresses or significant shear deformations. This characteristic of FRP jacketing theoretically leads to similar initial stiffness properties of FRP retrofitted buildings as the buildings without retrofit. In the current study, to validate this theoretical assumption, the initial stiffness characteristics, and thus, the potential seismic demands were investigated through forced vibration tests on two identical full-scale substandard reinforced concrete buildings with or without FRP retrofit. Power spectral density functions obtained using the acceleration response data captured through forced vibration tests were used to estimate the modal characteristics of these buildings. The test results clearly showed that the natural frequencies and the mode shapes of the buildings are quite similar. Since the seismic demand is controlled by the fundamental vibration modes, it is confirmed using vibration-based full-scale tests that the seismic demands of RC buildings remain unchanged after CFRP jacketing of columns. Furthermore, the damping characteristics were also found similar for both structures.

Key Words
CFRP; forced vibration test; reinforced concrete; retrofitting; seismic demand

Address
Pinar Inci: Department of Civil Engineering, Istanbul Kultur University, Istanbul, Turkey
Caglar Goksu: Faculty of Civil Engineering, Istanbul Technical University, Istanbul, Turkey
Erkan Tore: Department of Civil Engineering, Balikesir University, Balikesir, Turkey
Ergun Binbir: Faculty of Civil Engineering, Istanbul Technical University, Istanbul, Turkey
Ali Osman Ates: Department of Civil Engineering, Faculty of Technology, Gazi University, Ankara, Turkey
Alper Ilki: Faculty of Civil Engineering, Istanbul Technical University, Istanbul, Turkey

Abstract
Moment-resisting frames (MRFs) are among the most conventional steel structures for mid-rise buildings in many earthquake-prone cities. Here, a simplified performance-based methodology is proposed for the seismic collapse capacity assessment of these buildings. This method employs a novel multi-mode pushover analysis to determine the engineering demand parameters (EDPs) of the regular steel MRFs up to the collapse prevention (CP) performance level. The modal combination coefficients used in the proposed pushover analysis, are obtained from two metaheuristic optimization algorithms and a fitting procedure. The design variables for the optimization process are the inter-story drift ratio profiles resulting from the multi-mode pushover analyses, and the objective values are the outcomes of the incremental dynamic analysis (IDA). Here, the collapse capacity of the structures is assessed in three to five steps, using a modified IDA procedure. A series of regular mid-rise steel MRFs are selected and analyzed to calculate the modal combination coefficients and to validate the proposed approach. The new methodology is verified against the current existing approaches. This comparison shows that the suggested method more accurately evaluates the EDPs and the collapse capacity of the regular MRFs in a robust and easy to implement way.

Key Words
collapse prevention (CP); IDA; modal combination rules; moment resisting steel frames; optimization process; seismic collapse capacity assessment

Address
Mohammad M. Maddah, Sassan Eshghi and Alireza Garakaninezhad: Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), No. 21, Arghavan St., North Dibaji, Farmanieh. Tehran, Iran

Abstract
This research effort examines the flow behavior and heat transfer assessment of water carrying iron (iii) oxide magnetic fluid due to a rotating and moving plane lamina under the influence of magnetic dipole. The effect of rotational viscosity and magnetic body force is taken into consideration in the present study. The involvement of the moving disk makes a significant contribution to the velocity distribution and heat transfer in rotational flow. Vertical movement of the disk keeps the flow unsteady and the similarity transformation converts the governing equation of unsteady flow into nonlinear coupled differential equations. The non-dimensional equation in the present system is solved through the finite element procedure. Optimizing the use of physical parameters described in this flow, such results can be useful in the rotating machinery industries for heat transfer enhancement.

Key Words
ferrofluid; heat transfer; magnetic field; rotating and moving disk

Address
Anupam Bhandari: Department of Mathematics, School of Engineering, University of Petroleum & Energy Studies (UPES), Energy Acres Building, Bidholi, Dehradun- 248007, Uttarakhand, India


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2022 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-2-736-6800 (SCS, EAS, WAS, ANR) +82-42-828-7995 (GAE, SEM, SSS, CAC) Fax : +82-2-736-6801, Email: info@techno-press.com