现浇预应力连续箱梁的施工工艺及质量控制档

现浇预应力连续箱梁的施工工艺及质量控制

摘 要:对预应力桥梁工程的施工工艺进行进一步的探讨和研究,同时对现浇连续箱梁需要注意的施工细节提出建议。

关键词:现浇箱梁;施工;工艺

1 工程概况(阜朝高速公路K443+780平安地公铁立交桥为例)

K443+780平安地公铁立交桥,桥长100 m,分左右双幅桥,单幅宽为12. 50 m,跨径为30+40+30 m,其中中跨为40 m,分别上跨锦承铁路及地方公路,上部结构采用预应力混凝土现浇连续箱梁,纵向采用四层预应力钢绞线,梁高由1. 50 m过渡到2. 5 m;横向设置两层预应力钢绞线,底层间距90 cm,上层间距60 cm;竖向设置精轧螺纹预应力钢筋,间距60 cm。下部结构采用桩基础、承台,方柱式墩、肋板台。 2 现浇箱梁施工工艺及质量控制 2.1 地基处理

第1、3孔在桥跨与桥宽范围内,将场地平整,采用18 t以上振动压路机碾压4~5遍,回填碎石50~100 cm使地面高程距箱梁底高程距离约6. 0 m。压实度不小于90%,按横向间距0. 9 m,布置20 cm×20 cm的水平枕木,使压力扩散,确保支架在施工中不发生变形与失稳。地基回填后,开挖一定数量的排水沟,防止雨水对支架底部的浸泡。 2.2 支架搭设及支座安装

(1)支架布置:第1、3孔支架采用标准碗扣式脚手架,该支架轻巧,拼装方便,为保证支架的强度及整体稳定性,支架采用四体品字形双层结构排列,支架底部垫20 cm×15 cm水平方与地面之间铺一层石屑或小石子找平。支架之间用的钢管将门架纵横交叉联结,内部及外侧用钢管作剪刀撑,并用钢丝绳对称斜拉,在箱梁肋板,横隔板位置处支架加密1倍,悬臂板部分可适当减少一些。上托顶架铺设方木,其支架高度可按地形及门式脚架调整搭设,利用上托调整预拱度。

第2孔为跨铁路桥孔,按照铁路部门的要求确保铁轨两侧的净距不少于8. 5 m的要求,在铁轨两侧做监时钢支架,基础挖深2. 0 m,回填1. 0 m石渣,再浇筑1. 0 m的钢筋混凝土,并在每侧各放三个钢支架,上面纵向采用桁架片做纵梁,采用45b工字钢做横梁,间距0. 9 m。

(2)支架验算:钢管脚手架的稳定性检算强度验算,根据建筑施工扣件式脚手架安全技术规范,模板支架主要检算立杆稳定性。支架步距及纵距0. 9m、横距均按0. 9m检算。计算时主要考虑的荷载包括梁体钢筋混凝土自重、模板自重、支架自重、施工人员及机具重量、混凝土灌注振捣等。经验算采用稳定性满足要求方可进行施工。

跨越铁路上方的钢支架纵、横梁强度验算,计算时主要考虑的因素是梁体钢筋混凝土自重、模板自重、施工人员及机具重量、混凝土灌注振捣等,经验算纵、横梁强度满足要求后方可进行施工。

支架搭设完后,在墩柱及台身上用经纬仪准确测放出支座中心点位置,并按照设计图纸要求安装支座。 2.3 支架预拱度设置

预拱度计算公式:f=f1+f2,其中f1为支架弹性变形;f2为梁体挠度预拱度,最大值设在梁的跨中位置,并按抛物线形式进行分配,算得各点的预拱度值后,通过支架上的可调丝杆顶托或底座对底模进行调整。 2.4 模板的制作、安装及支架的预压

支座安装合格后,依据图纸尺寸加工并安装箱梁底模板,底模板钢模板,侧模板采用优质进口竹胶合板(1. 2 cm厚),表面光洁度、平整度、线条平顺均能满足美观要求,其刚度强度能满足要求。

模板接缝处嵌填海绵条或采用胶带封缝,并设置斜撑和压脚,以防跑模和漏浆。模板安装前,检查其是否变形、污染。支架底模高程计入落地支架弹性、非弹性变形值,其他位置按抛物线设置预拱度,以确保箱梁的标高符合设计要求。预压完成后,卸去砂包,把模板清洗干净,并涂刷优质脱模剂。重新测量标高调整底板。 支架静预压:在支架搭设完成以后,应对支架进行预压,预压荷载不小于梁体钢筋混凝土重量的1. 2倍,预压采用砂(或土)袋预压,其荷载分布与现浇箱梁重量分布情况一致,预压期间在每跨设置五个断面15个观测点,预压前先测量复核支点标高,砂袋用吊机吊放到支架上,试压分三次水平加载,第一次试压重40%,第二次为40%,第三次全部加完,然后观测7 d,卸载按三次进行,第一次按试重的20%,第二次为40%,第三

次全部卸完,每个观测点在每一次加载(卸载)完了及全部加载完(卸载完)均要观测,全部加载完成后先每一天观测一次,若连续7 d观测结果在5 mm以内,则可以认为地基沉降基本稳定。 2.5 钢筋、波纹管、钢绞线安装

调整底板合格后、安扎钢筋、安扎时分两次,第一次安扎钢筋为底肋板,在底板及肋板浇筑混凝土后安扎箱顶及悬臂预埋钢筋,在浇筑箱顶板时,在顶板应力最小处(1/4跨)开1×1. 5 m天窗(每一箱1个)拆除箱内模板、支架后将天窗钢筋焊接好,并采用与箱梁同标号混凝土浇筑平整。

在安装绑扎完底板钢筋及横隔板骨架后,安放纵、横向、竖向波纹管、钢绞线安装完后,再绑扎肋板钢筋。钢绞线安装程序:先按其长度,编号穿入波纹管,分布在肋部位置,再将波纹管及应力钢束按坐标要素表准确定位,采用钢筋“#”字架1. 0 m间距将钢束固定,弯曲部位间距为0. 5 cm,重复检查,穿钢束时波纹管是否有破裂,波纹管接口处采用橡胶条或封口胶布包裹密封,外用铁丝扎紧,当钢筋与钢束位置发生矛盾时,钢筋让位于钢束,在箱梁波纹管顶峰处引出气孔, (用小胶管引出),安装好波纹管钢束后,重新检查其坐标位置是否符合要求,进行调整,后完善其他肋板及横隔板钢筋,待混凝土浇注后,及时将钢绞线在桥两头利用卷扬机来回拉动,施工时特别注意防止波纹管漏浆及压扁引起下一道工序的困难。

安放纵、横、竖向波纹管时一定要按照图纸给定的坐标进行,不能随意改动,发生预应力钢筋与普通钢筋有抵触的地方要以预应力钢筋为主,变动普通钢筋的位置。 2.6 混凝土搅拌、运输、浇筑及其养生

(1)混凝土由2台L1000强制式搅拌机搅拌,由搅拌站统一供给。配料由电子秤控制(已经过计量部门检测标定),并严格按照中心试验室提供的混凝土配合比搅拌,由4台8 m³搅拌车运输、采用泵送混凝土浇筑施工,配8台插入式振动棒振捣。

(2)箱梁混凝土分两次浇筑(第一层为底板及肋板根部50 cm高,第二层为肋板、顶板和悬臂板)。箱梁底板和肋板混凝土采用斜层法由低端向高端浇筑。并由低向高推进。混凝土初凝后,用钢丝刷拉毛,使其表面粗糙而平整、清洁。以便于桥面铺装混凝土的结合质量。第一层混凝土浇筑时采用插入式振捣器振捣,并振捣密实。同时每个工作班制取试块不少于5组。最后一层施工的混凝土,把二组试块放在箱梁上同条件下养护,采用覆盖养生。 2.7 预应力张拉

(1)在混凝土强度达到设计强度100%后,且龄期达到14 d后方可进行张拉。预应力钢束张拉严格按照设计图纸提供的张拉顺序和张拉控制应力进行。张拉设备在使用前须进行检查和校核。

(2)本桥预应力箱梁采用后张法,预应力筋为低松弛预应力钢铰线,张拉工艺根据设计图纸纵向预应力钢绞线采用两端同时张拉,横向预应力钢绞线采一端张拉,竖向预应力钢筋采用在梁顶面张拉。

(3)预应力张拉采用双控,以张拉力进行控制,以伸长量进行校核,实际伸长量值与理论伸长值之差若超过规范要求应暂停张拉,查明原因并采取措施加以调整后,再继续张拉。

(4)张拉设备校核:张拉机具与锚具配套使用,在进场使用前进行检查与校核,每台千斤顶与压力表、压力盒、测力计及其他装置,应具有±1%的读数精度。压力表精度不应低于1. 5级。千斤顶一般使用超过6个月或200次,以及在使用中出现不正常现象时,应重新校准。

(5)张拉筋制作:每根预应力钢筋应标签以编号及盘号或使用钢材的号码,钢绞线不得扭折、绞旋,不得松散,且每根钢绞线在构件每端要易于识别。钢绞线下料长度应把两端工作长度计算在内、张拉后钢绞线的切割用高速手砂轮切割机,外露长度35 mm。

(6)纵、横向钢铰线张拉操作程序为: 0→初应力(10%δk)→δk→测伸长度→油缸回零、测回缩量(持荷2 min)。 2.8 孔道压浆

(1)压浆前,先吹入无油份的压缩空气清洗管道,再用含0. 01 kg/L生石灰或氢氧化钙的清水冲洗管道,再以压缩空气吹干。

(2)用水泥制浆搅拌机制备符合要求的水泥浆。首先将水加入拌和机内,再放入水泥,经充分拌和后掺入掺加剂(如果需要), (压浆前须经过滤, )拌和应至少2 min,直至达到均匀的稠度为止。然后将压浆泵输出管

与一根压浆管的甲端相连接。

(3)启动活塞式压浆泵由甲端进浆,从乙端排气,直到乙端排气孔流出符合规定稠度的浓浆后,关闭乙端阀门,并保持不小于0. 5MPa的一个稳压期,该稳压期不少于2 min,然后关闭甲端阀门。

(4)间隔30~45 min,再从乙端压浆,从甲端排气,直到甲端排气孔流出符合规定稠度的浓浆后,关闭甲端阀门,并保持不小于0. 5MPa的一个稳压期,该稳压期不少于2 min,关闭乙端阀门。

(5)压浆施工过程中填写完备的压浆记录,包括每个管道的压浆日期、水灰比及掺加料、压浆压力、障碍事故细节及需要补做的工作。

(6)压满浆的管道应进行保护,使在一天内不受振动,管道内水泥浆注入后的48 h内,结构混凝土温度不得低于5℃,否则应采取保温措施;当白天气温高于35℃时,压浆宜在夜间进行。 2.9 封锚

为了保护外露的锚具不致锈蚀而失效,当灌浆完毕后,将外露部分进行清洗,并将端面混凝土凿毛,并绑扎钢筋。锚后钢筋网与预留钢筋点焊一体,然后安装模板,浇筑混凝土。压浆封锚后,待压浆强度达到80%后,拆卸支顶架。

2.10 支架、模板的拆除

在压浆强度达90%及封锚完成后拆除所有支架。拆除支架时从跨中开始对称向两头均匀拆卸,以便使桥体重量对称、均匀地由两端支座平均承担,同时预防箱梁因受力不均匀产生裂纹。拆除底模时防止损坏箱梁外观质量。 3 结束语

在施工过程中,应当根据图纸要求、施工设备、现场施工条件、等各方面情况综合考虑。认真、谨慎的做每一道施工工序,采取积极有效的措施,保证工程质量、节约成本、确保施工安全。

Prestressed continuous box girder construction technology and quality control Abstract: The construction technology of prestressed bridge engineering for further exploration and study, recommendations Cast - need to pay attention to construction details.Keywords: cast-in-place box girder; construction; craft a project overview (Fu toward the highway K443 +780 safely rail overpass as an example) K443 +780 safely rail overpass bridge length of 100 m, at about double the rate of bridge, a singlewidth of 50 m span is 30 +40 to +30 m, which in the span of 40 m, respectively, on cross-Jin Cheng rail and local roads, the superstructure of prestressed concrete Cast - vertical with fourlayer of prestressing strand, high beam transition from 50 m to 5 m; horizontal set of two-tier PC strand, the bottom spacing of 90 cm, the upper layer spacing of 60 cm; vertical settings finishing thread prestressed reinforcement, spacing of 60 cm.Substructure pile foundation, pile cap, square column piers, ribs, Taiwan.2 Cast - Construction technology and quality control 2.1 foundation to deal with the 1st and 3rd holes cross the bridge and the bridge width within the site preparation, more than 18 t vibratory roller RCC 4 to 5 times, backfill gravel 50 100cm so that the ground elevation from the elevation distance from the end of the box girder of about 6 0 m.The degree of compaction of not less than 90%, the horizontal distance of 9 m, 20 cm × 20 cm sleepers layout, so that the pressure diffusion, and to ensure that the stent does not occur in the construction of deformation and instability.Foundation backfill, excavation of a certain number of drains, to prevent the rain from soaking the bottom of the bracket.Installation of of 2.2 Scaffording and bearing bracket arrangement (1): 1, 3 hole bracket standard of scaffold, the stent lightweight, convenient

assembling, in order to ensure the strength and overall stability of the stent, the stent using the four-body and twin pairslayer structure arranged in the bottom of the bracket pad between the shop in the 20 cm × 15 cm horizontal with the ground layer of stone chips or gravel leveling.Steel pipe used in the bracket between the door frame vertical and horizontal cross-links, internal and lateral steel pipe scissors, and wire rope symmetrical cable-stayed box girder ribs, diaphragm position bracket encryption times a cantilever plate part may be appropriate to reduce thesome.On the care the top frame laying of square wood, the frame height according to the terrain and the gantry stand adjustment, erection, on child care to adjust the pre-camber.2 holes for the cross-rail bridge opening, in accordance with the requirements of the railway authorities to ensure that the rails on both sides of the spacing of not less than 8 5 m, the tracks on both sides of the steel bracket when the supervisor, basic deepened 2 0 m, backfilling a0 m gravel, and then pouring 1 0 m reinforced concrete, and on each side and put three steel frame above vertical truss piece stringers, 45b beam do beam spacing of 9 m.(2) stent checking: the stability of steel scaffolding Calculation strength calculation, construction fastener Scaffolding Safety Technical Code, the template bracket Calculation pole stability.Stent step away from the vertical distance. 9m horizontal distance at 0. 9m Calculation.The main consideration in the calculation loads include the weight of the beam reinforced concrete, templates weight, weight bracket, construction personnel and equipment weight, the pouring of concrete vibrators.Experience counted using the stability to meet the requirements before construction.Across the rail above the steel bracket longitudinal beam strength calculation, the main consideration in the calculation is the reinforced concrete of the beam weight, weight template, construction personnel and equipment weight, the pouring of concrete vibrators, experience counted longitudinal beam intensity to meet the requirements beforeconstruction.Scaffording after theodolite accurately measured in the pier columns and Taiwan who release bearing center position, and in accordance with design drawings require the installation of the bearing.2.3 stent pre-camber settings pre-camber of the formula: f = f1 + f2, where f1 is the the bracket elastic deformation; pre-camber of f2 for the beam deflection, the maximum located at the cross in the position of the beam, according to the parabolic form of allocated, regarded as the point of pre-camber value after adjustment by backwater or base of the adjustable screw on the bracket on the bottom die.Preloading bearings 2.4 template production, installation and bracket installation is qualified in accordance with sheet size processing and installation box girder end of template, the end of the template of steel formwork side of the template with high-quality imported bamboo plywood (2 cm thick), surface finish, flatness, and smooth lines can meet the aesthetic requirements, the stiffness strength to meet the requirements.Template seams filling them with a sponge or the use of tape Sealing and bracing and the presser foot to prevent run-mode and leakage of plasma.The installation of the

template, check whether the deformation of the pollution.Mode elevation end of the bracket included in the floor stand flexible, non-elastic deformation and other locations according to the parabolic set of pre-camber, to ensure the elevation of the box girder to meet the design requirements.Preloading is completed, to unload sand bags, clean template, and brushing quality release agent.Re-measured the elevation to adjust the base plate.Stent static preload: in response to stent the Scaffording after the completion of the pre-pressure, pre-pressure load is not less than 1.2 times the weight of the reinforced concrete beam, pre-pressure sand (or soil) bags preload, the load distribution andCast - weight distribution, pre-pressure period in each cross set up 15 observation points of the five sections, measured before preloading review fulcrum elevation, sand bags with crane crane into the bracket, pressure test three times the level of increaseupload, the first pressure test weight 40%, 40% in the second, third plus all finished, and then observing for 7 d, uninstall the press three times, first test weight of 20%, 40% in the second,three times to finish unloading all, each observation point in every load (uninstall) finished and all finished loading (uninstalled) are to be observed, all finished loading every day observation time after the first observations of consecutive for 7 days in 5mm or less, you can basically stable foundation settlement.2.5 bars, bellows, installation and adjustment backplane qualified strand reinforced Anza Anza time-division two, the first Anza reinforced bottom ribs, floor and ribs pouring concrete the Hou Anzha box top and cantilever pre-Buried reinforced in the pouring box roof when open 1 × 5 m skylight in the roof stress minimum at (1/4 cross) (each box 1) removal of the box templates, welded steel stent after skylight, and usingthe same label and the box girder concrete pouring formation.Installation banding finished the backplane reinforced diaphragm skeleton An indulgence, horizontal, vertical bellows strand after you install, and then lashing ribs reinforced.Strand installation procedure: first by its length, the number penetration bellows, and distribution in the ribs position, and then bellows and stress of steel beams in accordance with the coordinates of elements of accurate positioning, the use of reinforced \"#\" character frame 1 0 m spacingfixed steel beam, curved parts of the spacing of 5 cm, double check to wear steel beam bellows rupture, interface with rubber or sealing tape wrapped bellows seal, external wire truss, when reinforced with steel beamposition of conflict, reinforced in the steel beam, leads to stomata in the box girder bellows peak (with a small hose leads), install the bellows steel beam, re-check the coordinates of the location to meet the requirements, making adjustments,improve the other ribs and diaphragm reinforced concreting timely strand in the bridge two winch pulling back and forth, pay special attention to prevent the construction of the bellows leakage pulp and flattening caused by the difficulties of the next process.An indulgence, horizontal, vertical bellows must be in accordance with the drawings given coordinates, can not tamper with the occurrence of prestressed steel reinforced conflict prestressed reinforced the main changes in the position of

ordinary reinforcement.2.6 The concrete mixing, transportation, placement, and health (1) concrete mixing by 2 L1000 compulsory mixer unified supply to the mixing station.Ingredients (metrology department has been testing calibration) is controlled by an electronic scale, and in strict accordance with the Central Laboratory of the concrete mix ratio mixing, 4 sets of 8 m³ mixer transport, the use of pumped concrete placement and construction, with eight plug-in vibratorvibrators.(2) concrete box girder twice pouring (the first layer is the root of the floor and ribs 50 cm high, the second layer of ribs, roof and cantilevered plate).The box girder bottom and ribs of concrete pouring oblique layer method from low to high end.By low-to high-propulsion.The initial setting of concrete with a wire brush nap, so that the surface is rough and smooth, clean.The combination of quality for concrete bridge deck pavement.The first layer of concrete pouring plug-in vibrators vibrators, vibrating compaction.Each work shift system to take the test block at least five groups.The last layer of the construction of concrete, two sets of test block on the box girder conservation under the same conditions, the coverage of health.2.7 prestressed tension (1) the strength of concrete to meet the design strength of 100%, and the age of 14 d before tensioning.Prestressed Steel pull in strict accordance with the design drawings provided by the tension sequence and tension control stress.Tensioning equipment before use to check and check.(2) prestressed box girder of the bridge with post-tensioned prestressing tendons for low relaxation prestressed steel hinge line tensioning process both ends of the tension, the transverse prestressing steel twist longitudinal prestressing strand according to the design drawingstension, one end of line mining, vertical prestressed reinforced with the beam top surface tension.(3) prestressed tension dual-control, control tensile force, elongation, check the difference of the actual elongation value and theoretical value of elongation to exceed regulatory requirements should be suspended tension, identify the reasons for and, and then continue to take measures to adjust the tension.(4) The tensioning device check: tensioning equipment and anchorage supporting the use of inspection and checking before the approach to use, each jack and pressure gauge, pressure cell, dynamometer and other devices, with ± 1% of reading accuracy.The pressure gauge accuracy should not be less than 1.5.Jack is generally used for more than six months or 200 times, as well as irregularities in the use, re-calibration.(5) stretching production: each prestressed reinforced tag number and plate number or use the number of steel strand shall not kink, twist rotation, shall not be loose, and each strand at each end of the componenteasy to identify.The expected length of the next strand should be the length of the both ends of the work taken into account, the strand tensioned cutting cutting machine with high-speed hand wheel, the exposed length of 35 mm.(6) the longitudinal and transverse steel hinge line tension operating procedures as follows: 0 → initial stress (10% δk) → δk → measurement the Elongation → cylinder back to zero, measured back Amount (loading for 2 min).2.8 Duct Grouting (1) grouting ago, blown into the oil-free

compressed air clean the pipes, and then containing 0 or 0.01 kg / L lime or calcium hydroxide, rinse with water pipes, and then blow dry with compressed air.(2) was prepared using cement pulp mixer to meet the requirements of the cement slurry.Water added to the mixer, then add the cement, mixed with a mixing agent (if required) after full mixing (grouting shall be subject to filtering,) mixing should be at least 2 minutes until it reaches a uniform consistency so far.Then the pressure pump output tube connected with a grouting tube A Duanxiang.(3) to start the piston pressure pump slurry into the A-side, the exhaust from the B-side, until the B-side vent out of the thick paste of required consistency, turn off the B-side valve, and maintain not less than 0. 5MPaa regulator of the regulator of not less than 2 min, the A-side and then close the valve.(4) 30 for 45 min intervals, from the B-side grouting, exhaust from the A-side until the A side vent out of compliance with the provisions of the consistency of thick syrup, turn off the A-side valve and maintain not less than 0. 5MPaa regulator of the regulator of not less than 2 min, turn off the B-side valve.(5) The grouting process, fill out the complete record of grouting, including grouting date of each pipe, the water-cement ratio and mixing materials, grouting pressure, obstacles accident details and the need to complement the work done.(6) The pressure of full-slurry pipeline should be protected, so that in one day from vibration, structural concrete temperature shall not be less than 5 ° C within 48 h after the grout injection pipe or insulation measures should be taken; when the daytime high temperature35 ° C, grouting should be carried out at night.2.9 anchor in order to protect the exposed anchorage will not rust and void when the grouting is completed, the exposed parts of the cleaning, and the face of concrete cutting hair, and steel banding.Anchor steel mesh and set aside the reinforced spot one, and then install the template, pouring concrete.Grouting seal anchor and after the grouting intensity of 80%, disassemble roof rack.2.10 bracket, removal of the template in the grouting intensity of 90% and removal of all stents after the completion of the seal anchor.Removal of the stent from a cross symmetry to the two uniform demolished, so that the weight of the bridge symmetry, the average bear evenly on both ends of the bearing, prevention of box girder due to uneven cracks.The base mold is removed to prevent the appearance quality of the damaged box girder.3 Conclusion During the construction process, it should be according to drawings, construction equipment, on-site construction conditions, and other aspects taken into account.Seriously and carefully done every construction process, and take effective measures to ensure project quality, cost savings and to ensure construction safety.