鋼筋混凝土T形梁及梁—板組合體的耐火性能研究
發(fā)布時間：2018-09-16 20:03
【摘要】：鋼筋混凝土結(jié)構(gòu)的耐火研究和耐火設(shè)計以往大多都是針對獨立構(gòu)件進行的，忽略了結(jié)構(gòu)中相鄰構(gòu)件之間的相互約束效應(yīng)，這與結(jié)構(gòu)的真實火災(zāi)行為存在明顯差異。近年來，，國內(nèi)外學(xué)者開展了具有端部約束的鋼筋混凝土梁、柱的耐火性能研究，相比以往獨立構(gòu)件無疑是明顯進步。除端部約束外，桿系構(gòu)件沿其長度方向還可能受到其它相鄰構(gòu)件的約束，進而對其火災(zāi)行為產(chǎn)生不同程度的影響（例如，梁側(cè)樓板不可避免地會對梁的火災(zāi)行為產(chǎn)生影響），但國內(nèi)外對此還鮮見研究報道。作為初步探討，本文以鋼筋混凝土梁及其相鄰樓板作為研究對象，從明火試驗、數(shù)值模擬、參數(shù)分析和實用計算方法等方面，初步考察了鋼筋混凝土T形梁及梁-板組合體的耐火性能。本文的主要工作和結(jié)論如下： 1.開展了6根足尺鋼筋混凝土簡支T形梁和2根對比矩形梁的明火試驗，考察了荷載比、板寬等參數(shù)對簡支T形梁高溫破壞特征、高溫變形及耐火極限的影響趨勢。試驗表明：荷載比較大時隨著板寬增加，簡支T形梁的耐火極限總體上隨之增大；板寬相同時隨著荷載比增加，簡支T形梁的耐火極限減小。 2.利用經(jīng)過前人和試驗數(shù)據(jù)驗證過的SAFIR軟件，開展了鋼筋混凝土簡支T形梁的耐火極限增大系數(shù)分析，考察了荷載比、梁跨高比、梁受拉縱筋配筋率、梁保護層厚度、板保護層厚度、板寬、板厚、板受拉縱筋配筋率等參數(shù)對該增大系數(shù)的影響規(guī)律；基于1296種工況的計算結(jié)果，建議給出了簡支T形梁的耐火極限增大系數(shù)的實用計算方法。研究表明：隨著荷載比和梁跨高比增加，簡支T形梁的耐火極限增大系數(shù)總體呈現(xiàn)出逐漸增大的趨勢；隨著梁受拉縱筋配筋率和梁保護層厚度增加，該增大系數(shù)逐漸降低；隨著板寬增加，該增大系數(shù)呈現(xiàn)出開始增長較快隨后基本保持不變的變化趨勢；隨著板保護層厚度增加，該增大系數(shù)迅速增大；但在常用取值范圍內(nèi)，板厚和板受拉縱筋配筋率對該增大系數(shù)影響較小。 3.在合理假設(shè)基礎(chǔ)上，分別推導(dǎo)給出了從空間框架中抽取出的梁-板組合體的板邊側(cè)向約束剛度和板邊轉(zhuǎn)動約束剛度的簡化計算公式；通過算例對比，驗證了上述簡化公式具有較好精度。 4.開展了9根具有梁端約束的足尺鋼筋混凝土T形梁的明火試驗，考察了升降溫作用下梁端軸向和轉(zhuǎn)動約束、荷載比、板寬等參數(shù)對約束T形梁高溫破壞特征、變形及內(nèi)力的影響趨勢。試驗表明：升降溫結(jié)束后約束T形梁存在較明顯的殘余軸壓力和一定的殘余軸向變形；隨著梁端軸向和轉(zhuǎn)動約束剛度比同時增加，約束T形梁的豎向撓度峰值總體差別不大；荷載比為0.3時，約束T形梁的軸壓力峰值隨板寬增加略有增大，但荷載比為0.5時，板寬增加對軸壓力峰值影響不明顯；板寬改變對約束T形梁的梁端彎矩和最大彎矩比影響有限。 5.利用SAFIR軟件，開展了同時具有梁端約束和板邊約束的鋼筋混凝土梁-板組合體的耐火性能分析，考察了梁端軸向約束剛度、梁端轉(zhuǎn)動約束剛度、板邊側(cè)向約束剛度、板邊轉(zhuǎn)動約束剛度、板寬等參數(shù)對具有邊界約束的梁-板組合體的高溫變形和內(nèi)力的影響規(guī)律。研究表明：隨著梁端軸向和轉(zhuǎn)動約束剛度以及板邊側(cè)向和轉(zhuǎn)動約束剛度的增加，梁軸力均有所增大；對梁端彎矩、梁跨中撓度和板中心點撓度而言，梁端轉(zhuǎn)動約束剛度的影響較大，而梁端軸向約束剛度、板邊側(cè)向約束剛度和板邊轉(zhuǎn)動約束剛度的影響有限；隨著板寬增加，梁軸力減小，但梁端彎矩、梁跨中撓度和板中心點撓度卻隨之增大。 6.由于鋼筋混凝土構(gòu)件的非線性行為，實際火災(zāi)中相鄰構(gòu)件之間的約束作用往往是時變的。由于時間和篇幅有限，作為考慮時變約束的第一步，本文對具有端部時變約束的矩形梁的耐火性能進行了計算分析，以期為后續(xù)具有時變約束的T形梁及梁-板組合體的耐火研究奠定基礎(chǔ)。首先考察了梁端時變軸向約束剛度和時變轉(zhuǎn)動約束剛度的變化趨勢，在此基礎(chǔ)上探討了時變約束對矩形梁升降溫全過程軸力和梁端彎矩的影響規(guī)律。研究表明：高溫下時變軸向約束梁的最大軸力比小于定常軸向約束梁的相應(yīng)值，軸向約束剛度比初值越小二者相差越大；高溫下時變軸向約束梁的最大梁端彎矩與定常軸向約束梁幾乎相同；時變轉(zhuǎn)動約束下梁軸力比和梁端彎矩隨升降溫時間的變化曲線都與定常轉(zhuǎn)動約束下的相應(yīng)曲線一致。
[Abstract]:Fire resistance research and fire resistance design of reinforced concrete structures are mostly carried out for independent members in the past, ignoring the mutual restraint effect between adjacent members in the structure, which is obviously different from the real fire behavior of the structure. In recent years, scholars at home and abroad have carried out the fire resistance of reinforced concrete beams and columns with end restraint. In addition to the end restraint, the member may also be restrained by other adjacent members along its length direction, which will have different degrees of influence on its fire behavior (for example, the beam side floor will inevitably have an impact on the beam fire behavior), but there is little research on this at home and abroad. As a preliminary study, this paper takes reinforced concrete beams and their adjacent floors as research objects, and preliminarily investigates the fire resistance of reinforced concrete T-shaped beams and beam-slab composites from the aspects of open fire test, numerical simulation, parameter analysis and practical calculation methods.
1. Six full-scale reinforced concrete simply supported T-shaped beams and two comparative rectangular beams were tested under open fire. The influence of load ratio, slab width and other parameters on high temperature failure characteristics, high temperature deformation and fire resistance limit of simply supported T-shaped beams were investigated. When the plate width is the same, the fire resistance of simply supported T beams decreases with the increase of load ratio.
2. By using the SAFIR software verified by predecessors and test data, the fire resistance limit increase coefficient of reinforced concrete simply supported T-shaped beam is analyzed. The influence of load ratio, beam Span-to-height ratio, ratio of longitudinal reinforcement, thickness of protective layer, thickness of protective layer, width, thickness and ratio of longitudinal reinforcement on the increase coefficient is investigated. Based on the calculation results of 1296 kinds of working conditions, a practical calculation method for the fire resistance limit increase coefficient of simply supported T-shaped beam is proposed. With the increase of thickness, the coefficient of increase decreases gradually; with the increase of slab width, the coefficient of increase presents a trend of rapid initial increase and then basically remains unchanged; with the increase of the thickness of the protective layer, the coefficient of increase increases rapidly; but within the range of commonly used values, the thickness of the slab and the ratio of longitudinal ribs have little influence on the coefficient of increase.
3. On the basis of reasonable assumptions, the simplified formulas for calculating the lateral restraint stiffness and the rotational restraint stiffness of the plate edge of the beam-plate composite extracted from the space frame are derived and given respectively.
4. Experiments on 9 full-scale reinforced concrete T-shaped beams with beam-end restraints were carried out under open fire. The effects of axial and rotational restraints, load ratio and plate width on the high-temperature failure characteristics, deformation and internal forces of the restrained T-shaped beams were investigated. The results show that the restrained T-shaped beams have obvious residual axes after heating and cooling. The peak value of the vertical deflection of the restrained T-shaped beam varies little with the increase of the ratio of axial and rotational restrained stiffness at the end of the beam. When the load ratio is 0.3, the peak value of the axial pressure of the restrained T-shaped beam increases slightly with the increase of the plate width, but when the load ratio is 0.5, the increase of the plate width has no obvious effect on the peak value of the axial pressure. The change of slab width has limited influence on the bending moment and maximum bending moment ratio of restrained T beam.
5. The fire resistance of RC beam-slab composite with both beam-end constraint and plate-edge constraint is analyzed by using SAFIR software. The axial restraint stiffness, beam-end rotational restraint stiffness, lateral restraint stiffness, plate-edge rotational restraint stiffness, plate width and other parameters of beam-slab composite with boundary constraint are investigated. The results show that the axial force increases with the increase of the axial and rotational restraint stiffness at the end of the beam, the lateral and rotational restraint stiffness at the edge of the plate, and the rotational restraint stiffness at the end of the beam has a greater influence on the bending moment at the end of the beam, the midspan deflection and the central point deflection of the plate, while the axial restraint stiffness at the end of the beam and the lateral and rotational restraint stiffness at the The influence of restraint stiffness in direction and rotational restraint stiffness at the edge of the plate is limited; with the increase of the width of the plate, the axial force of the beam decreases, but the bending moment at the end of the beam, the midspan deflection and the center deflection of the plate increase.
6. Because of the nonlinear behavior of reinforced concrete members, the constraints between adjacent members are often time-varying in actual fires. As the first step to consider time-varying constraints, the fire resistance of rectangular beams with end-varying constraints is calculated and analyzed in this paper, with a view to providing time-varying constraints for subsequent T-beams. Firstly, the variation trend of time-varying axial restraint stiffness and time-varying rotational restraint stiffness at the end of the beam is investigated, and then the influence of time-varying restraint on the axial force and bending moment at the end of the rectangular beam in the whole process of heating and cooling is discussed. The axial force ratio is smaller than the corresponding value of the stationary axial restrained beam, and the axial restrained stiffness ratio is smaller than the initial value. The maximum bending moment of the time-varying axial restrained beam at high temperature is almost the same as that of the stationary axial restrained beam. The corresponding curves are consistent.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TU375
本文編號：2244639
[Abstract]:Fire resistance research and fire resistance design of reinforced concrete structures are mostly carried out for independent members in the past, ignoring the mutual restraint effect between adjacent members in the structure, which is obviously different from the real fire behavior of the structure. In recent years, scholars at home and abroad have carried out the fire resistance of reinforced concrete beams and columns with end restraint. In addition to the end restraint, the member may also be restrained by other adjacent members along its length direction, which will have different degrees of influence on its fire behavior (for example, the beam side floor will inevitably have an impact on the beam fire behavior), but there is little research on this at home and abroad. As a preliminary study, this paper takes reinforced concrete beams and their adjacent floors as research objects, and preliminarily investigates the fire resistance of reinforced concrete T-shaped beams and beam-slab composites from the aspects of open fire test, numerical simulation, parameter analysis and practical calculation methods.
1. Six full-scale reinforced concrete simply supported T-shaped beams and two comparative rectangular beams were tested under open fire. The influence of load ratio, slab width and other parameters on high temperature failure characteristics, high temperature deformation and fire resistance limit of simply supported T-shaped beams were investigated. When the plate width is the same, the fire resistance of simply supported T beams decreases with the increase of load ratio.
2. By using the SAFIR software verified by predecessors and test data, the fire resistance limit increase coefficient of reinforced concrete simply supported T-shaped beam is analyzed. The influence of load ratio, beam Span-to-height ratio, ratio of longitudinal reinforcement, thickness of protective layer, thickness of protective layer, width, thickness and ratio of longitudinal reinforcement on the increase coefficient is investigated. Based on the calculation results of 1296 kinds of working conditions, a practical calculation method for the fire resistance limit increase coefficient of simply supported T-shaped beam is proposed. With the increase of thickness, the coefficient of increase decreases gradually; with the increase of slab width, the coefficient of increase presents a trend of rapid initial increase and then basically remains unchanged; with the increase of the thickness of the protective layer, the coefficient of increase increases rapidly; but within the range of commonly used values, the thickness of the slab and the ratio of longitudinal ribs have little influence on the coefficient of increase.
3. On the basis of reasonable assumptions, the simplified formulas for calculating the lateral restraint stiffness and the rotational restraint stiffness of the plate edge of the beam-plate composite extracted from the space frame are derived and given respectively.
4. Experiments on 9 full-scale reinforced concrete T-shaped beams with beam-end restraints were carried out under open fire. The effects of axial and rotational restraints, load ratio and plate width on the high-temperature failure characteristics, deformation and internal forces of the restrained T-shaped beams were investigated. The results show that the restrained T-shaped beams have obvious residual axes after heating and cooling. The peak value of the vertical deflection of the restrained T-shaped beam varies little with the increase of the ratio of axial and rotational restrained stiffness at the end of the beam. When the load ratio is 0.3, the peak value of the axial pressure of the restrained T-shaped beam increases slightly with the increase of the plate width, but when the load ratio is 0.5, the increase of the plate width has no obvious effect on the peak value of the axial pressure. The change of slab width has limited influence on the bending moment and maximum bending moment ratio of restrained T beam.
5. The fire resistance of RC beam-slab composite with both beam-end constraint and plate-edge constraint is analyzed by using SAFIR software. The axial restraint stiffness, beam-end rotational restraint stiffness, lateral restraint stiffness, plate-edge rotational restraint stiffness, plate width and other parameters of beam-slab composite with boundary constraint are investigated. The results show that the axial force increases with the increase of the axial and rotational restraint stiffness at the end of the beam, the lateral and rotational restraint stiffness at the edge of the plate, and the rotational restraint stiffness at the end of the beam has a greater influence on the bending moment at the end of the beam, the midspan deflection and the central point deflection of the plate, while the axial restraint stiffness at the end of the beam and the lateral and rotational restraint stiffness at the The influence of restraint stiffness in direction and rotational restraint stiffness at the edge of the plate is limited; with the increase of the width of the plate, the axial force of the beam decreases, but the bending moment at the end of the beam, the midspan deflection and the center deflection of the plate increase.
6. Because of the nonlinear behavior of reinforced concrete members, the constraints between adjacent members are often time-varying in actual fires. As the first step to consider time-varying constraints, the fire resistance of rectangular beams with end-varying constraints is calculated and analyzed in this paper, with a view to providing time-varying constraints for subsequent T-beams. Firstly, the variation trend of time-varying axial restraint stiffness and time-varying rotational restraint stiffness at the end of the beam is investigated, and then the influence of time-varying restraint on the axial force and bending moment at the end of the rectangular beam in the whole process of heating and cooling is discussed. The axial force ratio is smaller than the corresponding value of the stationary axial restrained beam, and the axial restrained stiffness ratio is smaller than the initial value. The maximum bending moment of the time-varying axial restrained beam at high temperature is almost the same as that of the stationary axial restrained beam. The corresponding curves are consistent.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TU375
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