용접수축이 강교량 캠버에 미치는 영향에 관한 연구

다국어 초록 (Multilingual Abstract)

The fabrication process of a steel bridge begins after the design stage, during which segmented blocks are manufactured in a factory, transported to the construction site, temporarily assembled, and then connected by bolting and/or field welding to complete the girders.
During factory fabrication, the camber specified at the design stage is considered, and an initial upward camber is pre-applied. The girders then undergo trial assembly before being transported to the site. At the site, the segmented steel bridge blocks are temporarily assembled in a stress-free condition, followed by bolted connections or field welding. Through measurement and adjustment of camber during this process, the steel bridge girders are ultimately fabricated.
When field welding is applied to girder connections, the girder length generally shortens due to welding shrinkage, and this length reduction can affect the camber of the girder.
In this regard, domestic design standards and construction specifications require that the camber induced by welding shrinkage be considered not at the design stage but at the construction, that is, fabrication stage. Accordingly, fabrication companies apply their own methods; however, because there has been little technical review of specific management measures for camber caused by welding shrinkage, the camber values resulting from welding shrinkage vary among fabricators and are largely based on experience.
Therefore, this study was conducted to establish a rational alternative for evaluating the effects of camber due to welding shrinkage by comparing and analyzing field-measured data from recently constructed steel bridges with results derived from empirical formulas, theoretical equations, and finite element analysis. The main contents and conclusions of this study are summarized as follows.
Among the welding-induced deformations, the deformation type that affects the bridge length is transverse shrinkage, and Sparagen’s empirical formula for butt welding was applied to this transverse shrinkage. A comparison between the measured camber values caused by welding shrinkage in the target bridge and the empirical results showed a significant discrepancy, indicating that camber values estimated using empirical formulas may overestimate the actual camber induced by welding shrinkage.
For the theoretical calculation of camber based on equivalent moments resulting from differences in field welding shrinkage, local welding shrinkage and strain were first calculated. Equivalent moments were then determined based on differences in welding shrinkage between cross-sections and eccentricity differences of the neutral axis. The camber variation was calculated by evaluating curvature and deflection due to the total equivalent moment, as well as overall deflection caused by the equivalent moment, thereby determining the camber change generated at each field-welded joint.
Thermal deformation analysis of field-welded joints using finite element analysis was performed with the general-purpose finite element program ABAQUS. Elasto-plastic thermal deformation analysis was conducted to account for welding heat input, and to improve analysis efficiency, a forced heat input method was applied at the location of the heat-affected zone (HAZ).
To predict the temperature distribution of materials under thermal loading, nonlinear heat transfer analysis was carried out in two stages: a rapid heating stage and a natural cooling stage. Structural analyses were performed by classifying the spacing between field welding support points into three cases: 1.5 m, 2.0m, and 3.0m.
As a result of comparing the actual measured camber values caused by welding shrinkage in the target bridge with those obtained from empirical formulas, theoretical equations, and finite element analysis, it was found that empirical formulas show considerable discrepancies from measured values due to the large number of variables involved, such as actual site conditions, welding conditions, member characteristics, and climatic factors. Therefore, it was deemed difficult to apply empirical formulas uniformly to all bridges. Although the theoretical and finite element analysis results showed slight differences from the measured values, the errors were within acceptable ranges. Consequently, this study is considered to provide a rational and practical alternative for evaluating the effects of welding-induced shrinkage on bridge camber during the steel bridge fabrication stage.

KEY WORDS : Camber, Upward camber, Welding shrinkage, Field weldingThe fabrication process of a steel bridge begins after the design stage, during which segmented blocks are manufactured in a factory, transported to the construction site, temporarily assembled, and then connected by bolting and/or field welding to complete the girders.
During factory fabrication, the camber specified at the design stage is considered, and an initial upward camber is pre-applied. The girders then undergo trial assembly before being transported to the site. At the site, the segmented steel bridge blocks are temporarily assembled in a stress-free condition, followed by bolted connections or field welding. Through measurement and adjustment of camber during this process, the steel bridge girders are ultimately fabricated.
When field welding is applied to girder connections, the girder length generally shortens due to welding shrinkage, and this length reduction can affect the camber of the girder.
In this regard, domestic design standards and construction specifications require that the camber induced by welding shrinkage be considered not at the design stage but at the construction, that is, fabrication stage. Accordingly, fabrication companies apply their own methods; however, because there has been little technical review of specific management measures for camber caused by welding shrinkage, the camber values resulting from welding shrinkage vary among fabricators and are largely based on experience.
Therefore, this study was conducted to establish a rational alternative for evaluating the effects of camber due to welding shrinkage by comparing and analyzing field-measured data from recently constructed steel bridges with results derived from empirical formulas, theoretical equations, and finite element analysis. The main contents and conclusions of this study are summarized as follows.
Among the welding-induced deformations, the deformation type that affects the bridge length is transverse shrinkage, and Sparagen’s empirical formula for butt welding was applied to this transverse shrinkage. A comparison between the measured camber values caused by welding shrinkage in the target bridge and the empirical results showed a significant discrepancy, indicating that camber values estimated using empirical formulas may overestimate the actual camber induced by welding shrinkage.
For the theoretical calculation of camber based on equivalent moments resulting from differences in field welding shrinkage, local welding shrinkage and strain were first calculated. Equivalent moments were then determined based on differences in welding shrinkage between cross-sections and eccentricity differences of the neutral axis. The camber variation was calculated by evaluating curvature and deflection due to the total equivalent moment, as well as overall deflection caused by the equivalent moment, thereby determining the camber change generated at each field-welded joint.
Thermal deformation analysis of field-welded joints using finite element analysis was performed with the general-purpose finite element program ABAQUS. Elasto-plastic thermal deformation analysis was conducted to account for welding heat input, and to improve analysis efficiency, a forced heat input method was applied at the location of the heat-affected zone (HAZ).
To predict the temperature distribution of materials under thermal loading, nonlinear heat transfer analysis was carried out in two stages: a rapid heating stage and a natural cooling stage. Structural analyses were performed by classifying the spacing between field welding support points into three cases: 1.5 m, 2.0m, and 3.0m.
As a result of comparing the actual measured camber values caused by welding shrinkage in the target bridge with those obtained from empirical formulas, theoretical equations, and finite element analysis, it was found that empirical formulas show considerable discrepancies from measured values due to the large number of variables involved, such as actual site conditions, welding conditions, member characteristics, and climatic factors. Therefore, it was deemed difficult to apply empirical formulas uniformly to all bridges. Although the theoretical and finite element analysis results showed slight differences from the measured values, the errors were within acceptable ranges. Consequently, this study is considered to provide a rational and practical alternative for evaluating the effects of welding-induced shrinkage on bridge camber during the steel bridge fabrication stage.

KEY WORDS : Camber, Upward camber, Welding shrinkage, Field welding

국문 초록 (Abstract)

강교량 제작단계는 설계 후 공장에서 블록 분절 제작하고, 현장으로 운반하여 현장지조립 과정을 거쳐 볼트이음 및 현장용접 후 거더를 완성하는 단계를 거친다.
캠버량은 공장 제작시에는 설계단계에서 제시한 캠버를 고려하여 솟음을 미리 주고 가조립 단계를 거쳐 현장으로 운반하며, 현장에서는 분절된 강교 블록을 무응력 상태에서 지조립 후 볼트연결 또는 현장용접을 실시하게 되는데 계측을 통하여 캠버를 조정하는 단계를 거쳐 강교량 거더를 제작하고 있다.
강재 거더 이음에 현장용접을 적용하면 용접수축에 의해 거더 길이가 일반적으로 짧아지게 되므로 거더 길이 수축량이 캠버에 영향을 줄 수 있다.
여기서 용접수축에 의한 캠버는 국내설계기준 및 공사시방서에서는 설계단계에서가 아닌 시공단계 즉 제작단계에서 고려하게 되어 있음에 따라 제작사에서 별도로 적용하고 있는데 용접수축으로 인한 캠버는 구체적인 관리방안 등의 기술적 검토가 거의 이루어지지 않고 있음에 따라 용접수축에 따른 캠버량이 제작사마다 상이하며, 경험에 의존하여 적용하고 있는 실정이다.
이에 이 연구에서는 최근 건설된 현장의 강교량을 대상으로 강교량의 용접수축으로 인한 캠버에 대해 현장에서 실측한 계측 데이터와 경험식, 이론식 및 유한요소해석을 통해 도출한 결과를 비교·분석하여 용접수축으로 인한 캠버 영향에 대해 합리적인 대안 마련을 위해 본 연구를 수행하게 되었으며, 본 연구의 주요 수행 내용과 결론은 다음과 같다.
용접에 의해 발생되는 용접변형 가운데 교량 길이에 영향을 주는 변형 형태는 횡방향 수축(transverse shrinkage)이며, 이 횡방향 수축에 대해 Sparagen의 맞대기 용접 경험식을 사용하였다. 본 연구대상 교량에 대해 용접수축으로 인한 캠버 실제 계측값과 비교한 결과 현저한 차이를 나타냄에 따라 경험식에 기초한 용접수축에 따른 캠버는 실제 용접수축에 의한 캠버에 비해 과대평가될 수 있는 것으로 검토되었다.
현장용접 수축량 차이 등가모멘트에 의한 이론 캠버 계산은 국부 용접수축량 계산 및 변형률을 계산 후 각 단면의 용접수축량 차이 및 단면 중립축 편심 차이로 인한 등가모멘트를 계산하였고 이를 통한 캠버 변화량 계산은 전체 등가모멘트에 의한 곡률과 처짐 계산 및 전체 등가모멘트에 의한 처짐 계산을 통해 각 현장용접 이음부에서 발생된 캠버 변화량를 계산하였다.
유한요소해석에 의한 현장용접부 열변형해석은 범용유한요소해석 프로그램인 ABQUS를 사용하여 용접 입열에 따른 현장용접부 열변형해석을 탄소성 열변형으로 실시하였고, 해석의 효율성을 확보하기 위해 열영향부(Heat Affected Zone)의 위치에 강제 열 주입 방식을 적용하였다.
열부하에 따른 재료의 온도분포를 예측하기 위해 비선형 열전달 해석(Non-linear Heat Transfer Analysis)을 급속 가열단계와 자연냉각단계로 두 단계에 걸쳐 수행하였으며, 현장용접 지지점 간격을 1.5m, 2m. 3m 3가지 경우로 분류하여 구조해석을 수행하였다.
본 연구대상 교량의 용접수축으로 인한 캠버 실제 계측값과 경험식, 이론식, 유한요소 해석 값을 비교한 결과 경험식은 실제 현장 여건 및 용접 조건, 부재의 특성, 기후조건 등 변수가 많아 실측치와 상당한 차이를 보임에 따라 모든 교량에 일괄적으로 적용하기에는 곤란할 것으로 검토되었고, 이론식과 유한요소 해석 결과는 실측치와 약간의 오차는 있으나 허용 가능한 범위의 오차이므로 강교 제작단계에서 용접으로 인한 교량 수축 영향 고려시 본 연구가 그 해법을 도출하는 합리적인 대안이 될 수 있을 것으로 판단된다.


KEY WORDS : 캠버, 솟음, 용접수축, 현장용접, 처짐, 계측

목차 (Table of Contents)

• List of Tables ⅲ
• List of Figures ⅳ
• ABSTRACT ⅶ
• 제1장 서 론 1
• 1.1 연구배경 및 목적 1
• 1.2 연구내용 및 범위 3
• 제2장 국내․외 캠버 관련 규정 4
• 2.1 캠버의 정의 4
• 2.2 국내 캠버 관련 규정 6
• 2.3 국외 캠버 관련 규정 17
• 2.3.1 미국 관련 규정 17
• 2.3.2 호 주 24
• 2.3.3 일 본 25
• 제3장 현장용접 적용에 따른 강재 거더의 변화 특성 26
• 3.1 용접에 따른 용접수축 26
• 3.2 용접에 따른 캠버 변화량 29
• 3.3 강교량 현장용접에 따른 사례 조사(일본) 33
• 3.3.1 실제 교량 부재를 이용한 현장용접시험 33
• 3.3.2 현장시공 48
• 제4장 연구대상 교량의 용접수축 검토 56
• 4.1 연구대상 교량의 개요 56
• 4.2 연구대상 교량의 캠버 57
• 4.3 연구대상 교량의 제작 및 가설 59
• 4.3.1 연구 대상 교량의 용접 및 용접 수축량 59
• 4.3.2 용접수축에 따른 캠버 평가 68
• 제5장 결 론 81
• 5.1 결 론 81
• 5.2 향후 과제 81
• 참고문헌 82
• 국문초록 84