高温喷水冷却后型钢UHPC界面黏结性能研究

Bonding Performance of Steel‒UHPC After High Temperature with Water Cooling

摘要

为研究高温喷水冷却后型钢与超高性能混凝土（UHPC）的界面黏结性能，以受热温度T、型钢保护层厚度C_s、体积配箍率ρ_v、恒温时长t、冷却方式为变化参数，设计制作了12个型钢UHPC试件并进行高温冷却后的单调加载推出试验，记录高温后试件的表面特征及质量损失，观察单调加载破坏过程，获取荷载‒滑移曲线，分析其特征点黏结强度，以揭示不同设计参数对界面黏结性能的影响规律。结果表明：随着T的升高，冷却后试件颜色由深变浅，质量烧失率逐渐增大至4.48%；界面黏结强度不断退化，与常温工况相比，400 ℃高温后试件黏结强度损失超过50%；随着t的增加，界面黏结强度先升后降，恒温90 min时为最大；增大C_s和ρ_v能有效提高水冷后试件的界面黏结强度；与自然冷却试件相比，喷水冷却后型钢UHPC界面极限黏结强度τ_u、残余黏结强度τ_r均提高约30%。基于试验结果，提出了喷水冷却后型钢UHPC界面黏结强度计算方法，可为型钢UHPC组合结构的灾后性能评估及修缮加固提供依据。

Abstract

Objective Ultra-high-performance concrete (UHPC) is widely used due to its dense microstructure, which provides ultra-high mechanical properties. Under earthquake action, it has a strong synergistic deformation capacity with steel, ensuring that structures or components do not experience stress performance degradation due to early interface bonding failure. Fire is one of the important forms of urban disasters. UHPC is usually directly exposed to high-temperature environments, where high internal steam pressure results in numerous cracks and corner spalling, causing material performance degradation. Firefighting is an indispensable measure for urban building fires. During firefighting, the ambient temperature decreases rapidly. For UHPC with a dense microstructure, the internal temperature stress distribution is extremely uneven, which accelerates the expansion and even bursting of concrete cracks, resulting in unclear mechanisms for the deterioration of the interface bonding performance between UHPC and steel. Therefore, accurately understanding the degradation mechanism of the bonding performance at the steel‒UHPC interface after high temperature and water cooling is crucial for evaluating the seismic performance of building structures after fire extinguishing. Currently, no report addresses the interfacial bonding performance of steel‒UHPC after high-temperature water cooling. This study presents experimental research on the bond‒slip performance between steel and UHPC after high temperature and water cooling, revealing the degradation mechanism of bond‒slip performance. Methods The research findings on the mechanical properties of reinforced concrete after high-temperature exposure and the interfacial bonding performance with steel, along with the pretest results and existing research results, were considered. This study conducted tests under three temperature and cooling conditions, including room temperature, water cooling, and natural cooling. In addition, temperature (T), constant temperature duration (t), steel protective layer thickness (C_s), and volume reinforcement ratio (ρ_v) were selected as test design parameters. Monotonic push-out tests were conducted on twelve steel-UHPC specimens after high-temperature exposure with different cooling methods. The apparent characteristics and mass loss rate of the specimens after high-temperature exposure were recorded in the experiment, and the displacement slips at the loading end and free end were monitored during the loading process. Based on the experiments, the interfacial bonding performance between UHPC and steel after high-temperature exposure with water cooling was analyzed by examining the collected curve data and observed phenomena, and a calculation method for interfacial bonding strength was proposed to evaluate the bonding performance after firefighting. Results and Discussions The main results and discussions were as follows: 1) The surface features, including color and crack development, were observed. The mass loss rate was measured. As the temperature increased from 20 ℃ to 800 ℃, the color of the specimen changed from dark gray to grayish white, and the surface cracks gradually increased. As the temperature increased from 200 ℃ to 800 ℃, the mass loss rates were 1.60%, 2.54%, 4.00%, and 4.48%. 2) The process and morphology of bond failure were observed. The characteristics of the load-slip curves and the bonding strength of the corresponding characteristic points were analyzed. The surface cracks of the specimen developed outward along the original cracks after high-temperature exposure, including cracks along the 45° direction at the tip of the steel flange, cracks parallel to the flange, and cracks in the middle of the flange, and extended to the side of the concrete. The load-slip curves of all specimens roughly passed through three stages, namely the initial slip stage, the slip failure stage, and the stable slip stage, in which the chemical cementation force, mechanical biting force, and frictional resistance gradually acted and successively provided the bonding force at different stages. 3) The effects of temperature (20 ℃, 200 ℃, 400 ℃, 600 ℃, 800 ℃), cooling method (water cooling and natural cooling), constant temperature duration (60, 90, and 120 min), steel protective layer thickness (50 mm, 60 mm, and 70 mm), and volume reinforcement ratio (0.160%, 0.238%, and 0.317%) on the interfacial bonding performance between UHPC and steel were studied. Compared to normal temperature conditions, after exposure to temperatures of 200 ℃, 400 ℃, 600 ℃, and 800 ℃, the ultimate bonding strength decreased by 13.6%, 49.3%, 92.3%, and 98.2%, respectively, and the residual bonding strength decreased by 16.8%, 57.1%, 94.6%, and 98.9%, respectively. Compared to the constant temperature duration of 60 min, when the constant temperature duration reached 90 min, the ultimate bonding strength and residual bonding strength increased by 15.4% and 36.2%, respectively. When the constant temperature duration reached 120 min, the ultimate bonding strength and residual bonding strength decreased by 24.7% and 31.0%, respectively. When the steel protective layer thickness increased from 50 mm to 60 mm, the ultimate bonding strength increased by 15.2%, and the residual bonding strength increased by 1.25%. When it increased from 60 mm to 70 mm, the ultimate bonding strength increased by 7.75%, and the residual bonding strength increased by 11.3%. When the volume reinforcement ratio increased from 0.160% to 0.238%, the ultimate bonding strength increased by 7.7%, and the residual bonding strength increased by 25.4%. When it increased from 0.238% to 0.317%, the ultimate bonding strength increased by 25.9%, and the residual bonding strength increased by 25.3%. When the temperature was 400 °C, compared to natural cooling, the ultimate bonding strength and residual bonding strength of the specimens after water cooling were greater, with increases of 41.7% and 64.5%, respectively. 4) Based on the experimental results, a calculation method for the bonding strength after water cooling was proposed. Conclusions As the temperature increases from 20 ℃ to 800 ℃, the mass loss rate gradually increases to 4.48%, with the growth rate showing a trend of rapid initial increase followed by slower growth. The load-slip curves of all specimens generally pass through three stages, namely the initial slip stage, the slip failure stage, and the stable slip stage, during which chemical cementation force, mechanical interlocking force, and frictional resistance gradually take effect and successively provide bonding force at different stages. The bonding strength continues to degrade, and compared to normal-temperature conditions, the loss of bonding strength after 400 ℃ exceeds 50%. As t increases, the bonding strength first increases and then decreases, with the maximum bonding strength observed at a constant temperature duration of 90 minutes. Increasing C_s and ρ_v can effectively improve the bonding strength of the specimens. Compared to naturally cooled specimens, the ultimate bonding strength τ_u and residual bonding strength τ_r both increase by approximately 30% after water-spray cooling. The proposed calculation method can provide a basis for performance evaluation, repair, and reinforcement of steel‒UHPC composite structures after disasters.

Graphical abstract

关键词

型钢超高性能混凝土 / 高温作用 / 喷水冷却 / 推出试验 / 黏结‒滑移 / 黏结强度

Key words

steel reinforced ultra-high performance concrete / high temperature effects / spray cooling / pull-out test / bond‒slip / bond strength

本刊网刊

超高性能混凝土（UHPC）具有强度超高、延性较好等特点，在地震作用下与型钢的协同变形能力较强，保证了结构或构件不会因界面较早发生黏结破坏致使受力性能退化^[1‒2]。因此，研究型钢与UHPC的界面黏结性能具有重要意义，是揭示该类组合构件协同受力机理的关键所在。

常温下型钢与UHPC的界面黏结性能研究^[3‒6]均表明二者之间的黏结性能优于型钢普通混凝土，但未能准确反映建筑火灾中或火灾后的界面黏结性能。火灾已成为城市灾害的重要形式之一，已有研究^[7‒10]表明，UHPC历经火灾并自然冷却后，其残余抗压强度逐渐下降；Banerji^[11]、何倍^[12]等研究表明，高温后UHPC的弹性模量随温度的增加呈降低的趋势，且下降速率较普通混凝土快。Lyzwa^[13]、Sciarretta^[14]等研究表明，UHPC致密的微观结构易使基体产生爆裂现象，不同纤维类型及掺量可有效抑制高温爆裂并改善其性能。

消防喷水灭火是应对城市建筑火灾的重要举措，不同于高温后自然冷却，消防灭火中环境温度骤然下降，加剧了混凝土材料内部温度应力场的不均匀分布并产生大量的损伤裂缝，致使混凝土与型钢界面的黏结性能劣化。已有研究从材料^[15‒17]、界面^[18‒19]两个层次分别对高温后混凝土力学性能及型钢界面黏结性能进行了研究。郑钰涛等^[20]研究表明，当温度超过400 ℃后，喷水冷却条件下普通混凝土试块的抗压强度降幅更大。柯晓军等^[21]研究表明，与自然冷却相比，喷水冷却后再生混凝土残余强度呈先高后低、再高再低的变化趋势。Yu等^[22]研究表明，与自然冷却相比，水冷却条件下高性能混凝土单轴抗压强度下降幅度最大达到62.02%。Fayadh等^[23]研究表明：高强混凝土因水冷而发生劣化的临界点为400 ℃；随着温度的升高，试件的黏结强度和剪切刚度降低。Pang等^[24]研究表明，高温水冷后试件的极限和残余黏结强度随经历最高温度的升高均呈先降低后增加的规律。陈宗平等^[25]研究表明，受热温度不高于400 ℃时，喷水冷却条件下界面黏结强度较大，但高于400 ℃后，自然冷却方式下界面黏结强度较大。武芳文^[26]和Liu^[27]等研究了冷却方式对钢‒ECC组合梁受剪性能的影响，结果表明湿水冷却方式对组合梁受剪承载力折减作用较为显著，承载力下降较快。

综上，高温水冷后混凝土力学性能的退化机理较为复杂，一方面温度应力场分布不均；另一方面遇水后混凝土基体在高温下发生二次水化反应，致使高温水冷后型钢与UHPC的界面黏结性能退化规律不明晰。因此，通过设计高温喷水冷却后型钢UHPC界面推出试验，研究受热温度、恒温时长、保护层厚度、体积配箍率、冷却方式等参数对界面黏结性能的影响，揭示高温喷水冷却后型钢UHPC界面的黏结劣化机理，提出特征黏结强度计算公式，以期为型钢UHPC组合结构的灾后性能评估及修缮加固提供依据。

1 试验概况

1.1 试件设计

设计制作了12个型钢UHPC界面黏结试件并进行推出试验，以受热温度T、恒温时长t、型钢保护层厚度C_s、体积配箍率ρ_v、冷却方式为变化参数，研究喷水冷却后界面黏结性能的劣化机理，试件设计参数见表1。内置型钢选用Q355级HW 100 mm×100 mm×6 mm×8 mm宽翼缘H型钢；纵筋选用A12 mm的HRB400级钢筋；箍筋选用A6 mm、A8 mm的HPB300级钢筋；型钢埋置长度均为400 mm，试件上、下端部型钢分别伸出100、50 mm作为加载端、自由端。试件几何尺寸及构造如图1所示。

试验UHPC主要原料为P·O 52.5硅酸盐水泥、硅灰、粉煤灰、石英砂、镀铜平直钢纤维、水、减水剂，水胶比为0.18，具体配合比见表2，其中钢纤维基本物理特性见表3。各试件预留3个UHPC标准立方体试块，用于检测历经不同高温后的抗压强度；按《金属材料拉伸试验 第2部分：高温试验方法》（GB/T 228.2—2015）^[28]对型钢试件进行拉伸试验。高温后材料的力学性能见表4。

1.2 升温及喷水冷却过程

采用1 200 ℃快速高温炉对试件进行升温试验，平均升温速率为5 ℃/min^[29]。试件受热前，用防火石棉对试件裸露的型钢进行包裹，防止高温炉内的高温直接作用于型钢，高温试验设备如图2所示。待温度上升至目标温度并恒温结束后，立即取出并使用消防水枪进行四面循环喷水降温，保证均匀降温，待试件温度降至50 ℃以下停止冷却，喷水冷却过程如图3所示。升温及冷却过程中，及时记录试件产生的现象（气味、声音、水汽），喷水冷却后试件统一静置48 h，记录试件的质量损失，观察其表观（颜色、裂纹）变化。

1.3 加载方案

采用YAJ‒3000型微机控制电液伺服加载试验机进行单调推出试验，加载过程分为预加载和正式加载。加载装置如图4所示。预加载阶段，加载至10 kN后待仪表读数稳定后卸载，从而消除试件与装置之间的缝隙；正式加载阶段，加载端型钢滑移前，加载速率为10 kN/min；产生滑移后，加载速率降至5 kN/min，每级恒载1 min并及时记录裂缝开展情况。当滑移量显著增加，荷载不再显著变化时，认为推出试验终止。加载过程中，试件加载端、自由端的相对滑移量通过图4中的位移计测量获取。

2 高温试验分析

2.1 表观特征

试件经高温及喷水冷却后，其表观特征发生显著变化，如图5所示。由图5可知：

1）随着受热温度的升高，试件由深灰色变为灰白（棕）色，颜色由深变浅，表面裂纹逐渐增多。与常温相比，受热温度为200 ℃时，试件表面仅出现较少细微裂纹；受热温度为400～600 ℃时，试件表面由浅灰色变为灰白色，表面出现连续网状裂纹且裂纹较宽，同时出现黄棕色灼烧点和钢纤维灼烧裂纹；受热温度为800 ℃时，试件表面由灰白色变为灰棕色，试件表面裂纹交错相接，黄棕色灼烧点与钢纤维灼烧裂纹增多。

2）喷水冷却过程中，试件遇水瞬间发出“嘶嘶”声，同时产生白色烟雾，试件上、下端面型钢与UHPC基体界面处及高温后裂缝处不断有气泡冒出；温度越高，其表面产生的气泡越多，且持续时间越长。

2.2 质量损失

通过对比型钢UHPC试件高温前与高温喷水冷却后的质量，定义其质量烧失率I，计算公式如下：

{\rm I}=\frac{M-M_T}{M}\times \mathrm{100}\mathrm{\%}（1）

式中，M为高温前试件的质量，M_T 为高温喷水冷却后试件的质量。

试件质量烧失率I随温度T变化的曲线如图6所示。

由图6可知：

1）试件质量烧失率随温度的升高而逐渐增大。受热温度为200、400、600、800 ℃时，质量烧失率分别达到1.60%、2.54%、4.09%、4.48%。

2）受热温度T400 ℃时，质量损失增长速率先快后慢，原因是历经200 ℃的高温作用后，UHPC基体内自由水蒸发，水泥浆体中C‒S‒H凝胶中结合水蒸发，质量损失增长较快；历经200⩽T400 ℃高温时，UHPC基体内结合水进一步丧失，同时伴有Ca(OH)₂吸热性脱水，水分子一减一增致使质量损失增长相对较慢。

3）受热温度为400⩽T⩽800 ℃时，质量损失增长速率先快后慢，原因是历经400⩽T600 ℃高温时，水泥水化产生的Ca(OH)₂受热分解生成CaO和H₂O，同时也会与孔洞中的CO₂发生碳化反应，生成CaCO₃和H₂O，高温加剧了UHPC基体内结合水的蒸发，导致UHPC基体内产生孔隙和裂缝，使其质量损失增长较快；历经600⩽T⩽800 ℃高温时，在喷水冷却条件下，UHPC分解出的大量CaO等碱性氧化物，能够与自由水结合并重新生成Ca(OH)₂晶体，硅灰中SiO₂与Ca(OH)₂、自由水结合并重新生成水化硅酸钙（C‒S‒H）凝胶，致使质量损失率增长较慢。

3 推出试验分析

3.1 试件破坏过程

试件典型裂缝形态如图7所示。

由图7可知：1）加载初期，加载端和自由端均无滑移产生。加载至极限荷载的10%～30%时，加载端开始出现微小滑移；继续增大荷载，自由端界面开始产生滑移。接近极限荷载时，加载端、自由端滑移量不断增大，常温及高温试件均发出劈裂声，随即型钢被缓慢推出，同时伴随UHPC基体与型钢表面的摩擦声。

2）对于常温试件，接近极限荷载时，加载端和自由端位于型钢腹板的侧面出现细微裂缝，且随着荷载增大，裂缝沿端部向内延伸，同时试件表面中部出现细微裂缝；最终裂缝沿试件高度方向并未贯穿，自由端型钢UHPC界面处出现混凝土剥落现象。

3）对于高温试件，接近极限荷载时，加载端和自由端位于型钢翼缘的侧面开始出现细微裂缝，且随着荷载增大，裂缝沿端部向内延伸。在加载端与自由端面，高温作用后原有裂缝（沿型钢翼缘肢尖处45°方向裂缝、平行翼缘裂缝、翼缘中部裂缝）向外发展，并延伸至混凝土侧面。最终，试件表面中部未出现黏结裂缝，自由端型钢UHPC界面处出现混凝土剥落。

3.2 荷载‒滑移曲线

图8为试件加载端、自由端荷载‒滑移（P‒S）曲线。图8中，取加载端P‒S曲线峰值A点荷载记为极限荷载P_u，B点荷载记为残余荷载P_r，对应位移分别记为极限滑移S_u、残余滑移S_r；C点为加载结束点。由图8可知：

1）试件加载端与自由端的P‒S曲线呈现出相似的变化规律，自由端发生滑移的时间滞后于加载端，达到极限荷载P_u后曲线基本重合，残余荷载P_r维持在极限荷载的50%～80%。

2）试件P‒S曲线大致经历3个阶段，即初始滑移阶段、滑移破坏阶段、平稳滑移阶段。在初始滑移阶段，加载初期，加载端与自由端的型钢和UHPC基体发生弹性变形，变形不协调而产生极小的相对滑移，此时界面的化学胶结力逐渐增大；随着荷载的持续增大，型钢与UHPC界面间开始产生相对滑移，荷载与滑移大致呈线性增长，此时化学胶结力开始丧失。在滑移破坏阶段，达到极限荷载后，界面间化学胶结力全部丧失，此时型钢与UHPC基体微凹凸界面相互错接，型钢与UHPC基体界面间黏结力由机械咬合力和摩擦阻力提供。在平稳滑移阶段，达到残余荷载后，型钢与UHPC基体微凹凸界面不断滑移磨损，其裂缝发展与破坏形态稳定，加载端与自由端滑移基本保持一致，此时机械咬合力退出工作，界面间的黏结作用主要是摩擦阻力。

3）极限荷载过后，常温及受热温度为200 ℃的试件曲线下降较为平缓，受热温度高于200 ℃的试件曲线下降较陡。

通过对高温冷却后型钢UHPC推出试件的P‒S曲线规律的观察与归纳，建立了两类典型P‒S曲线，均可分为上升OA段、下降AB段、水平BC段，如图9所示。图9中：常温及T=200 ℃试件的P‒S曲线，归纳为第一类曲线，其中AB段为缓降段；T>200 ℃试件的P‒S曲线归纳为第二类曲线，其中AB段为陡降段。

3.3 特征黏结强度

定义与极限荷载P_u、残余荷载P_r对应的界面剪切应力分别为极限黏结强度τ_u、残余黏结强度τ_r。黏结强度τ计算公式如下：

\tau =\frac{P}{s{l}_{\mathrm{a}}}（2）

式中：P为荷载值；s为型钢截面周长；l_a为型钢埋置长度，取400 mm。

对于型钢混凝土试件，英国标准^[30]规定黏结强度取0.02f_c（f_c为混凝土抗压强度设计值）且不大于0.45 MPa；欧洲规范BS EN 1994‒1‒1:2004^[31]规定在锚固区内，黏结力取0.50 MPa。表5为试件加载端P‒S曲线的特征值。由表5可知：常温及受热温度不高于400 ℃的型钢UHPC试件的τ_u和τ_r介于0.40～2.21 MPa，均高于前述两规范关于黏结强度设计值的要求，仍具有较好的黏结性能，从而保证建筑结构的安全；受热温度超过400 ℃时，试件τ_u和τ_r介于0.02～0.17 MPa，均低于规范设计值要求，界面黏结性能严重退化，不能提供良好的协同工作性能。

3.4 参数影响分析

3.4.1 受热温度T

图10为受热温度对高温喷水冷却后试件（S1～S5）荷载‒滑移曲线及界面黏结强度的影响。由图10可知：

1）随着受热温度的升高，试件荷载‒滑移曲线极限荷载及对应的滑移量均逐渐减小，界面的残余变形能力逐渐降低。极限黏结强度τ_u、残余黏结强度τ_r不断减小，与常温（20 ℃）下黏结强度相比，经历200、400、600、800 ℃高温后τ_u分别降至常温的86.4%、50.7%、7.8%、1.8%，τ_r分别降至常温的82.3%、42.5%、5.4%、1.1%。

2）随着受热温度的升高，界面的τ_u、τ_r的下降趋势大致可分为慢降、快降、慢降3个阶段。a. 20 ℃⩽T200 ℃为慢降段，τ_u、τ_r降幅分别为13.6%、17.7%，原因是在经受200 ℃高温后UHPC基体内水泥水化反应更加充分，促进了硅灰和粉煤灰中的活性SiO₂与水泥水化产物Ca(OH)₂之间的火山灰反应，生成C‒S‒H凝胶，使得UHPC与型钢界面间的化学胶结力损失较少。b. 200 ℃⩽T600 ℃为快降段，τ_u、τ_r降幅分别为91.1%、93.5%，原因是在经受400 ℃⩽T600 ℃高温后，UHPC基体内快速的再水化反应持续进行，加剧了已有裂纹扩展及新裂纹的产生；基体内Ca(OH)₂、C‒S‒H等水化产物大量分解，其部分胶凝作用减弱；同时，随着高温损伤的不断增加，基体内钢纤维氧化以及喷水冷却时温度应力分布不均，促使裂缝和孔隙不断形成，使型钢与UHPC界面间的化学胶结力劣化严重。c. 600 ℃⩽T⩽800 ℃为慢降段，τ_u、τ_r降幅分别为76.5%、80.0%，原因是经历800 ℃高温作用后，UHPC基体内裂缝增多，但喷水冷却后未完全反应的水泥颗粒继续水化，部分水泥水化物与硅灰等活性矿物掺合料中的SiO₂重新生成水化晶体（水化硅酸钙），使界面间的化学胶结力在一定程度上有所恢复；同时，经受600 ℃高温后喷水降温，型钢表面易产生氧化层并形成凹凸不平的纹路^[32]，增强了界面间的机械咬合力和摩擦阻力。

3.4.2 恒温时长t

由预埋K型热电偶测温试验可知，炉内达到目标温度约30 min后，UHPC与型钢界面温度达到目标温度。图11为恒温时长t对水冷后型钢UHPC试件（S3、S6、S7）荷载‒位移曲线及界面黏结强度的影响。

由图11可知：

1）随着t的增加，试件极限荷载先增大后减小，说明历经400 ℃高温时，试件的临界恒温时长约为90 min。

2）t增至90 min时，τ_u、τ_r分别提高15.4%、36.2%，说明经受90 min恒温作用后，UHPC基体内水泥水化反应充分，促进了硅灰中活性SiO₂与水泥水化产物Ca(OH)₂间的火山灰反应，生成C‒S‒H凝胶，凝胶颗粒不断增多并填充了高温裂缝，提升了UHPC基体的致密性，增强了型钢与UHPC界面间的化学胶结力，使其极限黏结强度增大，且水冷后UHPC基体收缩变形大，增强了型钢与UHPC界面间的机械咬合力，摩擦阻力增大。

3）t增至120 min时，τ_u、τ_r分别降低34.8%、49.4%，说明随着恒温时长的增加，基体内Ca(OH)₂等水化产物大量分解，同时钢纤维受热膨胀严重，纤维与基体间产生拉应力导致界面处裂缝充分发展，桥连作用减弱，型钢与UHPC界面间化学胶结力损失严重，抵消了一部分UHPC基体遇水收缩变形产生的增强作用，致使界面黏结强度下降。

3.4.3 型钢保护层厚度C_s

图12为型钢保护层厚度C_s对试件（S3、S8、S9）界面荷载‒滑移曲线及黏结强度的影响曲线。图12（b）中，定义C_s与型钢截面高度h之比为相对保护层厚度。

由图12可知：随着C_s的增大，试件极限黏结荷载P_u及残余黏结荷载P_r逐渐增大，荷载‒滑移曲线下降段较为平缓。试件的黏结强度随C_s的增加而增大，由50 mm增至60 mm时，τ_u提高15.2%，τ_r提高1.25%；由60 mm增至70 mm时，τ_u提高7.75%，τ_r提高11.3%。C_s对界面黏结性能的作用主要通过约束型钢的横向膨胀变形实现，随着C_s的增大，混凝土对型钢的约束作用增强，高温后型钢变形变小，其界面间的化学胶结力及摩擦阻力增大，试件的黏结强度随之增大。

3.4.4 体积配箍率ρ_v

图13为体积配箍率ρ_v对试件（S11、S3、S10）荷载‒滑移曲线及界面黏结强度的影响曲线。由图13可知：随着ρ_v的增加，试件的推出荷载逐渐增大，下降段更为平缓；随着ρ_v的增大，高温后界面黏结强度逐渐增大，τ_u、τ_r平均增幅约为16.74%、25.4%，说明在平稳滑移阶段，箍筋对混凝土提供较强的侧向和横向约束作用，提高了界面的摩擦阻力，对残余黏结强度τ_r的提升较为明显。

3.4.5 冷却方式

图14为冷却方式对试件（S3、S12）荷载‒滑移曲线及界面黏结强度的影响。

由图14可知：喷水冷却方式下，试件荷载‒滑移曲线具有较大的黏结强度，且下降段相对较为平缓；受热温度为400 ℃时，喷水冷却方式下界面τ_u、τ_r均大于自然冷却方式下的黏结强度，分别提高了41.7%、64.5%。这是因为喷水冷却作用下，型钢与UHPC的力学性能发生改变，UHPC中部分水化产物Ca(OH)₂大量脱水，重新生成水化硅酸钙，使得界面间的化学胶结力在一定程度上有所恢复；喷水冷却后型钢的屈服强度略有提高，型钢表面形成粗糙纹路，且由于瞬间的热胀冷缩，使得界面间摩擦阻力与机械咬合力增大，其界面间黏结强度增大。

4 黏结强度计算方法

为探讨高温后喷水冷却方式下型钢UHPC界面黏结强度的计算方法，本文以T、t、C_s、ρ_v为影响参数，根据试验实测值，以极限黏结强度τ_u和残余黏结强度τ_r为回归统计对象，计算如下：

\begin{array}{c}{\tau }_{\mathrm{u}}=\mathrm{0.004}\mathrm{29}T-\mathrm{2.248}\mathrm{45}\times {\mathrm{10}}^{-\mathrm{5}}{T}^{\mathrm{2}}+\mathrm{1.798}\mathrm{83}\times {\mathrm{10}}^{-\mathrm{8}}{T}^{\mathrm{3}}-\\ \mathrm{0.003}\mathrm{81}t+\mathrm{1.764}\mathrm{63}\frac{C_{\mathrm{s}}}{h}+\mathrm{2.369}\mathrm{77}{\rho }_{\mathrm{v}}+\mathrm{0.690}\mathrm{68}\end{array}（3）

\begin{array}{l}{\tau }_{\mathrm{r}}=\mathrm{0.001}\mathrm{24}T-\mathrm{1.422}\mathrm{74}\times {\mathrm{10}}^{-\mathrm{5}}{T}^{\mathrm{2}}+\mathrm{1.266}\mathrm{17}\times {\mathrm{10}}^{-\mathrm{8}}{T}^{\mathrm{3}}-\\ \mathrm{0.001}\mathrm{9}t+\mathrm{0.958}\mathrm{16}\frac{C_{\mathrm{s}}}{h}+\mathrm{2.301}\mathrm{8}{\rho }_{\mathrm{v}}+\mathrm{0.815}\mathrm{94}\end{array}（4）

利用式（3）、（4），对高温喷水冷却后型钢UHPC的界面黏结强度进行计算，结果见表6。计算值与试验值的对比关系如图15所示。由表6和图15可知：极限黏结强度τ_u计算值与试验值之比的平均值为1.02，标准差为0.14，变异系数为0.13；残余黏结强度τ_r计算值与试验值之比的平均值为1.03，标准差为0.38，变异系数为0.37，说明采用本文所提回归公式计算得到的极限黏结强度和残余黏结强度与试验值吻合较好。

5 结 论

1）随受热温度的升高，型钢UHPC试件由深灰色变为灰白（棕）色，表面裂纹扩展延伸且数量增多；质量烧失率逐渐增大，以400 ℃高温为临界温度，其增长速率均呈先快后慢的变化趋势。

2）随着荷载增大，型钢腹板、翼缘侧面以及高温产生的裂缝都逐渐向外延伸，最终在UHPC表面形成交错连接的裂缝区域；加载结束后，自由端截面处均出现混凝土剥落现象。

3）试件的荷载‒滑移曲线大致经历了初始滑移、滑移破坏、平稳滑移3个阶段，初始滑移阶段黏结力主要由化学胶结力提供，滑移破坏阶段黏结力主要由机械咬合力和摩擦阻力提供，平稳滑移阶段主要由摩擦阻力提供；当受热温度达到400 ℃后，其滑移破坏阶段下降趋势较为陡峭，黏结力快速下降。

4）随着T的升高，界面黏结强度逐渐下降，受热温度达到800 ℃时，τ_u、τ_r仅为常温下的1.8%、1.1%；随着t的增加，界面黏结强度先升后降，恒温90 min时τ_u、τ_r达到最大；增大C_s可有效提高界面黏结强度，随着C_s的增大，τ_u的提高幅度逐渐减小，而τ_r的增加幅度逐渐增大；增大ρ_v可以显著提高界面残余黏结强度τ_r；喷水冷却后试件的极限黏结强度及残余黏结强度均大于自然冷却后的黏结强度。

5）基于试验数据，提出了喷水冷却后型钢UHPC极限黏结强度和残余黏结强度的计算方法，其计算值与试验值吻合较好。

参考文献

[1] Zhang Jianrui, Meng Xiangyu, Song Jiaxin,et al.Push-out tests of interfacial bond slip between H-shaped steel and ultra-high performance concrete[J].Structures,2023,57:105268. doi:10.1016/j.istruc.2023.105268

[2] Cao Xuan, Xie Xiangdong, Zhang Tianyi,et al.Bond-slip behavior between high-strength steel tube and ultra-high performance concrete[J].Structures,2023,47:1498‒1510. doi:10.1016/j.istruc.2022.11.052

[3] Huang Zhenyu, Lin Gan, Huang Xinxiong,et al.Bond-slip constitutive model and numerical simulation of shaped steel embedded in UHPC[J].Industrial Construction,2024,54(3):143‒152.

[4] 黄振宇,林坩,黄新雄,等.型钢‒超高性能混凝土黏结滑移本构模型与数值模拟[J].工业建筑,2024,54(3):143‒152.

[5] Ming Ming, Zheng Shansuo, Zheng Hao,et al.Experimental study on bond-slip behavior between encased steel and high-performance fiber concrete[J].Engineering Mechanics,2020,37(8):148‒157. doi:10.6052/j.issn.1000-4750.2019.09.0555

[6] 明铭,郑山锁,郑淏,等.型钢高性能纤维混凝土粘结滑移性能试验研究[J].工程力学,2020,37(8):148‒157. doi:10.6052/j.issn.1000-4750.2019.09.0555

[7] Huang Zhenyu, Huang Xinxiong, Li Weiwen, et al. Bond-slip behaviour of H-shaped steel embedded in UHPFRC[J]. Steel and Composite Structures, 2021,38(5):563‒582.

[8] Ming Ming, Zheng Shansuo, Zhang Yixin,et al.Experimental study on the bond-slip behavior and stress transfer mechanism between shaped steel and high-performance fiber-reinforced concrete[J].Structures,2021,34:5013‒5028. doi:10.1016/j.istruc.2021.09.014

[9] Yang Ting, Yang Yekai, Liu Zhongxian,et al.Investigation on mechanical properties of ultra-high performance concrete after high temperature[J].Engineering Mechanics,2025,42(4):97‒109.

[10] 杨婷,杨烨凯,刘中宪,等.高温后超高性能混凝土力学性能试验研究[J].工程力学,2025,42(4):97‒109.

[11] Peng Gaifei, Yang Juan, Shi Yunxing.Experimental study on residual mechanical properties of ultra-high performance concrete exposed to high temperature[J].China Civil Engineering Journal,2017,50(4):73‒79.

[12] 朋改非,杨娟,石云兴.超高性能混凝土高温后残余力学性能试验研究[J].土木工程学报,2017,50(4):73‒79.

[13] Sumitomo G S, Pimentel L L, Jacintho A E P G A,et al.Study of ultra-high performance concrete mechanical behavior under high temperatures[J].Materials,2024,17(17):4212. doi:10.3390/ma17174212

[14] Chen H J, Yu Yilin, Tang Chaowei.Mechanical properties of ultra-high performance concrete before and after exposure to high temperatures[J].Materials,2020,13(3):770. doi:10.3390/ma13030770

[15] Banerji S, Kodur V.Effect of temperature on mechanical properties of ultra-high performance concrete[J].Fire and Materials,2022,46(1):287‒301. doi:10.1002/fam.2979

[16] He Bei, Zhang Hongen, Zhu Xinping,et al.Review on mechanical properties and degradation mechanism of ultra-high performance concrete in elevated environment[J].Journal of the Chinese Ceramic Society,2024,52(11):3470‒3481.

[17] 何倍,张红恩,朱新平,等.高温环境下超高性能混凝土力学性能及劣化机制研究进展[J].硅酸盐学报,2024,52(11):3470‒3481.

[18] Lyzwa J, Zehfuss J.Experimental investigations of ultra-high performance concrete exposed to natural fires[J].Fire Safety Journal,2021,125:103399. doi:10.1016/j.firesaf.2021.103399

[19] Sciarretta F, Fava S, Francini M,et al.Ultra-high performance concrete(UHPC) with polypropylene(Pp) and steel Fibres:Investigation on the high temperature behaviour[J].Construction and Building Materials,2021,304:124608. doi:10.1016/j.conbuildmat.2021.124608

[20] Chen Zongping, Ban Maogen, Zhou Ji.Influence of cooling methods on residual mechanical properties of concrete after exposed to high temperatures[J].Journal of Experimental Mechanics,2022,37(1):52‒62.

[21] 陈宗平,班茂根,周济.冷却方式对高温后不同类型混凝土残余力学性能的影响研究[J].实验力学,2022,37(1):52‒62.

[22] Xu Longkang, Yang Yong, Zhang Yang,et al.Estimation of stress-strain constitutive model for ultra-high performance concrete after high temperature with an deep neural network based method[J].Construction and Building Materials,2023,408:133690. doi:10.1016/j.conbuildmat.2023.133690

[23] Wu Fangwen, He Lanqing, Duan Junqi,et al.Mechanical properties and microscopic damage mechanism of PVA‒ECC after high-temperature cooling[J].Journal of Harbin Institute of Technology,2024,56(9):140‒149.

[24] 武芳文,何岚清,段钧淇,等.PVA‒ECC高温冷却后力学特性与微观损伤机理[J].哈尔滨工业大学学报,2024,56(9):140‒149.

[25] Chen Zongping, Zhou Wenxiang, Xu Jinjun.Experimental study on bond‒slip behavior of steel reinforced high strength concrete after high temperature[J].Journal of Building Structures,2015,36(12):106‒115. doi:10.14006/j.jzjgxb.2015.12.013

[26] 陈宗平,周文祥,徐金俊.高温后型钢高强混凝土界面黏结滑移性能试验研究[J].建筑结构学报,2015,36(12):106‒115. doi:10.14006/j.jzjgxb.2015.12.013

[27] Zhou Chunheng, Cao Jiazhang, Chen Zongping.Bond behavior of steel-recycled aggregate concrete interface after high temperatures and spraying water cooling[J]. Frontiers in Materials,2021,8:643510. doi:10.3389/fmats.2021.643510

[28] Zheng Yutao, Li Yucheng, Peng Chenxin.Effect of different cooling methods on mechanical properties of concrete after high temperature[J].Journal of Water Resources and Water Engineering,2019,30(4):189‒194.

[29] 郑钰涛,李玉成,彭晨鑫.高温后不同冷却方式对混凝土力学特性的影响[J].水资源与水工程学报,2019,30(4):189‒194.

[30] Ke Xiaojun, Yang Chunhui, Su Yisheng,et al.Influences of cooling methods on mechanical properties of recycled aggregate concrete after exposure to high temperature[J].Journal of Building Materials,2017,20(5):794‒800.

[31] 柯晓军,杨春辉,苏益声,等.冷却方式对高温后再生混凝土力学性能的影响[J].建筑材料学报,2017,20(5):794‒800.

[32] Yu Zhenpeng, Yang Qi, Zhang Jun,et al.Research on uniaxial mechanical performance of high-performance concrete after high temperature rapid cooling and damage mechanism analysis[J].Journal of Building Engineering,2024,86:108921. doi:10.1016/j.jobe.2024.108921

[33] Fayadh O K, Qasim O A, Farhan O S.Effects of concrete types,elevated temperatures,and different cooling technique on concrete compressive strength[J].Journal of Engineering Science and Technology,2021,16(3):1916‒1931.

[34] Pang Shaohua, Huang Yuming, Chen Zongping,et al.Bond-slip performance of water cooling steel-reinforced high-strength concrete after high temperature[J].Case Studies in Construction Materials,2023,19:e02271. doi:10.1016/j.cscm.2023.e02271

[35] Chen Zongping, Dai Shangqin, Wang Cheng,et al.Experimental study on bonding performance of steel reinforced recycled aggregate concrete after high temperature fire-fighting sprinkler[J].Journal of Natural Disasters,2020,29(2):1‒9.

[36] 陈宗平,戴上秦,王成,等.高温后消防喷水型钢再生混凝土黏结性能试验研究[J].自然灾害学报,2020,29(2):1‒9.

[37] Wu Fangwen, Shaoxuan Mai, Cui Xuan,et al.Experimental study on shear performance of steel‒ECC composite beams after high temperature cooling[J].Journal of Building Structures,2024,45(2):38‒51.

[38] 武芳文,买少轩,崔璇,等.钢‒ECC组合梁高温冷却后受剪性能研究[J].建筑结构学报,2024,45(2):38‒51.

[39] Liu Shuo, Wu Fangwen, Zheng Wenzhong, et al. Study on the shear behaviour of steel‒concrete composite beams after elevated temperature and water cooling[J]. Archives of Civil and Mechanical Engineering, 2024, 24(2):126. doi:10.1007/s43452-024-00927-4

[40] 国家质量监督检验检疫总局,中国国家标准化管理委员会. 金属材料拉伸试验 第2部分:高温试验方法:GB/T 228.2—2015 [S].北京:中国标准出版社,2016.

[41] 国家质量监督检验检疫总局,中国国家标准化管理委员会. 建筑构件耐火试验方法 第1部分:通用要求:GB/T 9978.1—2008 [S].北京:中国标准出版社,2009.

[42] British Standards Institution. BS 540025:2005,Steel,concrete and composite bridges.Part 5:Code of practice for the design of composite bridges [S].London:BSI,2005.

[43] European Committee for Standardization. EN 1994‒1‒1:2004, Design of composite steel and concrete structures. Part 1‒1:General rules and rules for buildings [S].Brussels:CEN,2004. doi:10.1680/dgte4.31517

[44] Yang Caijun, Zhang Chuntao.Experimental research on mechanical properties of water-cooled Q355 steel after being subjected to high temperature[J].Industrial Construction,2021,51(11):165‒170.

[45] 杨财骏,张春涛.高温水冷却后Q355钢材力学性能试验研究[J].工业建筑,2021,51(11):165‒170.

基金资助

国家自然科学基金项目(52278172)

河南省粮油仓储建筑与安全重点实验室开放课题（2020KF‒B06）

河南省教育厅自然科学项目(24A560006)