Experimental Research on Impact Resistance of Partially Precast Concrete Beams

Huimin Mao,Xueyuan Yan,Chenchen Zong,Cihang Lin,Xuhong Liu 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.9

A building may be subjected to multiple accidental loads during its service-life. Partially precast concrete (PC) beam is a primary force-bearing member. When subjected to an impact load, its impact resistance will significantly affect the overall safety of the structure. In this study, five PC beams were designed and manufactured, and drop-hammer impact tests were performed. The influences of impact mass and impact height on the failure mode and the dynamic response of the component under different loading conditions were examined. The typical failure mode of the test beam under a dynamic load was derived from the failure mode and crack distribution. The dynamic responses such as impact force, supporting reaction force, and displacement–time-history curve were obtained by the test. With increasing impact energy, the peak impact force increased from 3,353 to 3,708 kN, the peak mid-span displacement increased from 33.6 to 47.3 mm, and the residual mid-span displacement increased from 11.9 to 15.1 mm. Subsequently, the law of energy dissipation in the impact process was analyzed using the combined curves of the impact force-mid-span displacement and support reaction force-mid-span displacement. Furthermore, the result obtained by the integration of the reaction force-displacement curve in the middle of the span is more suitable for evaluating the overall energy consumption of the beam. The vibration energy and internal energy of the beam itself account for the primary part of the remaining energy.

구조 진동 측정을 이용한 프레스 성형품 넥 결함 검사기술 타당성 연구

곽재혁,국형석,김흥규,최현철,양우호 한국소음진동공학회 2018 한국소음진동공학회 논문집 Vol.28 No.6

If defects occur in a press-formed article, the mechanical properties change and the vibration characteristics may change. In particular, it is not difficult to prove a crack defect on the basis of structural vibration measurement. The purpose of this study was to develop a defect inspection technique that can quickly determine whether the neck of a press-formed article is defective by measuring the simple structural vibration of the neck, which indicates a defect of a fine press-molded product, rather than a crack. The press moldings used in the experiment were automobile front door panels; the structural vibration of the front door panels was measured with an impact hammer test. The frequency response function measured by the impact hammer test was obtained by the vibration frequency analysis program LMS Test.lab. With this method, we compared and analyzed whether there is a significant difference from a front door panel in which a defect is generated, on the basis of the natural frequency dispersion that many normal front door panels without defects have in the corresponding mode. A total of 10 normal front door panels and two necked defective front door panels were tested. The observable mode frequencies of the normal front door panel and the necked front door panel were shown in terms of sigma levels to determine if there is a significant natural frequency difference. In addition, normal door panels without necks were divided into two groups with a difference of approximately 9 months in production. SPSS software was used for the statistical validation t-test. From this experiment, the results will become the basic data of a test method to detect the defective necks of press-formed parts through natural frequency measurement.

소석회 첨가에 따른 투수성 아스팔트 혼합물의 성능 평가

문성호,김도완,전은비,이상염,윤태섭 한국방재학회 2014 한국방재학회논문집 Vol.14 No.6

The objective of this paper is to investigate the properties for permeability and dynamic resistance of the porous asphalt mixtureswhich consist of either liquefied lime or powder lime and is to conduct Impact Resonance Test (IRT) and Impact Hammer ResonanceTest (IHRT) to proof the public trust in the point of civil engineering. For the performance of permeability, Constant Head PermeabilityTest based on Korean Industrial Standards of KS F 2322 was utilized for deducting the permeability coefficients of Hydratedlimeporous asphalt specimens. Non-destructive impact tests were conducted for the dynamic moduli. The resonance frequencies ofmixtures can be obtained from the frequency analysis for high frequency impact. From the comparison of the resonance frequenciesand the dynamic moduli obtained from IRT and IHRT, Root Mean Squared Error (RMSE) values of dynamic moduli obtained fromIHRT indicated the maximum value of 1.16 GPa comparing to the results of IRT. The result of error analysis between IRT and IHRTresults has Mean Absolute Percentage Error (MAPE) which was under 8%. To figure out the effect of additives, compared eachporous asphalt mixture by using the result of constant head permeability test and dynamic moduli. 본 논문의 목적은 액상형 소석회와 분말형 소석회를 첨가한 아스팔트 혼합물의 투수성능과 동적 저항 성능을 평가하는 것이다. 또한동적 저항 성능을 파악하기 위한 비파괴충격파 시험의 공신력을 입증하기 위해 IRT 및 IHRT를 수행하였다. 아스팔트 혼합물의 투수성능을 파악하기 위해 한국산업 규격 KS F 2322에 의거한 정수위 투수 시험을 실시하였다. 동적 저항 성능 능력 평가를 위하여 비파괴 충격 시험을 수행하였으며, 혼합물의 공진 주파수를 측정하여 IRT와 IHRT에서 얻은 동탄성계수를 비교하였다. 그 결과 IRT시험과IHRT시험 결과가 최대 1.16 GPa의 RMSE와 8% 이내의 MAPE 내에 있다는 것을 확인하였다. 첨가제의 영향을 파악하기 위하여 각아스팔트 혼합물의 동탄성계수 결과와 정수위 투수 시험 결과를 비교 분석하였다.

비파괴시험에 의한 콘크리트 항만시설물의 주요 물성치 평가

이진학(Yi, Jin-Hak),한상훈(Han, Sang-Hun),박우선(Park, Woo-Sun) 한국해안해양공학회 2011 한국해안해양공학회 논문집 Vol.23 No.1

항만 리모델링을 위한 콘크리트 시설물에 대한 평가가 필요하며, 특히 리모델링이 결정된 경우에는 소파 블럭이나 케이슨 블록 등에 대한 재활용 여부를 평가하여 재활용이 가능할 경우에는 유용하는 것이 경제적인 리모델링에 도움이 될 수 있다. 이 연구에서는 콘크리트 항만시설물에 대한 건전성 평가 및 재활용성 평가를 위하여 기존의 초음파 속도법을 비롯하여 슈미트 해머를 이용한 반발경도법, 충격반향법, 표면파 속도법 등의 비파괴시험을 실시하였다. 국내 5개 항만에 대하여 비파괴시험 및 시편을 채취하였으며, 채취한 시편에 대한 압축강도 시험을 수행하여 비파괴시험 결과와 비교하였다. 비파괴시험결과와 압축강도 시험을 통하여 콘크리트 재료의 탄성계수와 압축강도 등을 평가하였다. Recently harbor remodeling projects are seriously considered to enhance the loading and unloading capability of old container terminals and to make decrepit ports as eco-friendly harbor and waterfront spaces in many countries. In such a case, quantitative and qualitative evaluations on concrete harbor facilities are mandatory to determine the current structural integrity condition of aged materials. Once the remodeling project is determined to be carried out, the reusability of individual structural members and facilities including caissons, cell-blocks, and tetra-pods need to be decided based on the simple and economic visual inspection and/or nondestructive testing. In this study, the systematic quantitative evaluation procedure for determining the structural integrity condition and the reusability is studied based the nondestructive testing and evaluation methods. Conventional methods including Schmidt hammer test and ultrasonicpulse velocity methods and elastic wave based methods including impact echo test and surface wave test are applied to the old harbor facilities in five different sites. The compressive tests are also carried out to determine the elastic modulus and compressive strength of concrete materials.

Dynamic Characteristics for Traditional Wooden Structure in Korea by using Impact Hammer Test

Park, Sung-Ah,Choi, Jae-Sung,Min, Kyung-Won 단국대 부설 리모델링연구소 2010 리모델링 연구소 논문집 Vol.8 No.2

This paper presents an investigation on dynamic characteristics of Heunginjimun through both ambient vibration and impact hammer tests. Heunginjimun, treasure No. 1 in Seoul, Korea, is a traditional wooden structure. Ambient vibration test is performed and spectrum analysis of time history is carried out to identify dominant frequency contents of Heunginjimun. Impact hammer test is undertaken to find the natural frequency of Heunginjimun with frequency response functions and phase information. Test results show that natural frequencies are 1.lHz, l.5Hz, 3.2Hz and 4.2Hz in two principal axes. Natural frequencies obtained by the tests are used to find the lateral stiffness of Heunginjimun. Simple dynamic models for Heunginjimun are suggested based on the moment resistance from joint beams and the restoring force due to column rocking. Lateral stiffness is found with identified natural frequencies and simple dynamic models.

충격하중에 의한 용접구조물의 강도 증가에 관한 연구

이천수,양영수 韓國工作機械學會 2000 한국생산제조학회지 Vol.9 No.3

It is well known that during the oxygen cutting process residual thermal stresses are produced in weldment. The local non-uniform heating and subsequent cooling, which takes place during any welding process, causes complex thermal strains and stresses to finally lead to residual stresses exceed to the yield stress. High tensile stresses combined with applied structural load in the region near the welded joint can give rise to distortion, brittle fracture, change of the fatigue strength and stress corrosion cracking. The appropriate treatment of the welded component which reduces the peak of the welding residual stresses is believed to lower risk of the fracture during the service of the structure. In this study, the impact loading in oxygen cutting frame was applied to reduce the residual stress. After applying the impact loading, redistribution of resid-ual stress was measured by cutting method and the effect of fatigue was tested.

지수창함수를 사용한 임팩트햄머 실험에서 주파수응답함수의 왜곡과 개선책

안세진,정의봉 한국소음진동공학회 2003 한국소음진동공학회 논문집 Vol.13 No.5

Exponential window function Is widely used In impact hammer testing to reduce leakage error as well as to get a good S/N ratio. The larger its decaying rate is, the more effectively the leakage errors are reduced. But if the decay rate of the exponential window is too large, the FRF is distorted. And the modal parameters of the system can not be exactly identified by modal analysis technique. Therefore, it is a difficult problem to determine proper decay rate in impact hammer testing. In this paper, amount of the FRF distortion caused by exponential window is theoretically uncovered. A new circle fitting method is also proposed so that the modal parameters are directly extracted from impulse response spectrum distorted by the exponential-windowed impulse response data. The results by the conventional and proposed circle fitting method are compared through a numerical example.

원위치 동적강성 분석기의 개발 및 성능평가

김동주,변용훈 한국농공학회 2019 한국농공학회논문집 Vol.61 No.2

Stiffness characteristic of subgrade is one of the most important aspects for the design and evaluation of pavement and railway. However, adequatefield testing methods for evaluating the stiffness characteristics of the subgrade have not been developed yet. In this study, an in-situ dynamic stiffnessanalyzer (IDSA) is developed to evaluate the characteristics of subgrade stiffness along the depth, and its performance is evaluated in elastic materialsand a compacted soil. The IDSA consists of a falling hammer system, a connecting rod, and a tip module. Four strain gauges and an accelerometerare installed at the tip of the rod to analyze the dynamic response of the tip generated by the drop of hammer. Based on the Boussinesq’s method,the stiffness and Young’s modulus of the specimens can be calculated. The performance of IDSA was tested on three elastic materials with differenthardness and a compacted soil. For the repeatability of test performance, the dynamic signals for force and displacement of the tip are averaged fromthe hammer impact tests performed five times at the same drop height. The experimental results show that the peak force, peak displacement, and theduration depend on the hardness of the elastic materials. After calculating the stiffness and elastic modulus, it is revealed that as the drop height ofhammer increases, the stiffness and elastic moduli of MC nylon and the compacted soil rapidly increase, while those of urethanes less increase.

A PROCEDURE FOR GENERATING IN-CABINET RESPONSE SPECTRA BASED ON STATE-SPACE MODEL IDENTIFICATION BY IMPACT TESTING

SUNG GOOK CHO,JINTAO CUI,김두기 한국원자력학회 2011 Nuclear Engineering and Technology Vol.43 No.6

The in-cabinet response spectrum is used to define the input motion in the seismic qualification of instruments and devices mounted inside an electrical cabinet. This paper presents a procedure for generating the in-cabinet response spectrum for electrical equipment based on in-situ testing by an impact hammer. The proposed procedure includes an algorithm to build the relationship between the impact forces and the measured acceleration responses of cabinet structures by estimating the state-space model. This model is used to predict seismic responses to the equivalent earthquake forces. Three types of structural model are analyzed for numerical verification of the proposed method. A comparison of predicted and simulated response spectra shows good convergence, demonstrating the potential of the proposed method to predict the response spectra for real cabinet structures using vibration tests. The presented procedure eliminates the uncertainty associated with constructing an analytical model of the electrical cabinet, which has complex mass distribution and stiffness.

A PROCEDURE FOR GENERATING IN-CABINET RESPONSE SPECTRA BASED ON STATE-SPACE MODEL IDENTIFICATION BY IMPACT TESTING

Cho, Sung-Gook,Cui, Jintao,Kim, Doo-Kie Korean Nuclear Society 2011 Nuclear Engineering and Technology Vol.43 No.6

The in-cabinet response spectrum is used to define the input motion in the seismic qualification of instruments and devices mounted inside an electrical cabinet. This paper presents a procedure for generating the in-cabinet response spectrum for electrical equipment based on in-situ testing by an impact hammer. The proposed procedure includes an algorithm to build the relationship between the impact forces and the measured acceleration responses of cabinet structures by estimating the state-space model. This model is used to predict seismic responses to the equivalent earthquake forces. Three types of structural model are analyzed for numerical verification of the proposed method. A comparison of predicted and simulated response spectra shows good convergence, demonstrating the potential of the proposed method to predict the response spectra for real cabinet structures using vibration tests. The presented procedure eliminates the uncertainty associated with constructing an analytical model of the electrical cabinet, which has complex mass distribution and stiffness.