建筑结构抗震英文文献.doc

Study on safety appraisement and strengthening technology of masonry structure buildings damaged in wenchuan earthquakeYing Ma , Yongsheng Yi,Shuchun Zhou ,Yuexing Zhu , and Qigang Jiang1) Graduate Student ,School of Architecture & Civil Engineering ,CUMT ,China2) General Manager , Xuzhou Architecture design & research institute CO ,LTD ,China3) Associate Professor ,School of Architecture & Civil Engineering ,CUMT , China4) Director ,Xuzhou Construction Engineering testing Center, China5) Chief Engineer ,Xuzhou Construction Engineering Testing Center, ChinaM,,,Abstract: Referring to the appraisement of masonry structure buildings in Mianzhu City, this paper studied the safety inspection methods, seismic capability appraisement process based on summarizing and analyzing of its earthquake damages; also, the strengthening technology was discussed. Most earthquake damages of masonry structure building were cracks on walls: the most common damages were X-shaped cracks on walls under or between windows(outer longitudinal) and incline cracks along corners of opening for doors and windows, then X-shaped, incline cracks on load bearing cross and inner longitudinal walls, also few horizontal and vertical cracks can be found. Considering the demand of seismic capability and reliability appraisement ,inspections were primarily carried out on structural measures of the mass structure. Compound seismic capability and reliability of building was appraised according to the results of first level appraisement, its performance in earthquake and values of strengthening .Strengthening of buildings damaged in earthquake must separate members to be repaired or strengthened according to their available bearing capacity; and also economic conditions and beauty appearance should be taken into consideration. All we do could be used as a reference to seismic and reliability appraisement or strengthening design of buildings damaged in earthquake or ordinary ones.Keywords: Wenchuan Earthquake, Masonry structure building, Seismic appraisement, Appraiser of reliability, Seismic strengthening of building1. INTRODUCTIONAt 14:28pm on May 12 2008, a devastating earthquake (M8.0) stuck Sichuan, a province in southwest of China. mianzhu city, 35km to the epicenter (wenchuan country), is one of the regions which were most severely hit I the disaster. Most severely damaged or collapsed buildings are of masonry structure. After the earthquake, we have appraised the seismic capability and reliability of buildings in Mianzhu, most of which are of masonry structure. In our paper, with a case study we appraised, studies were carried out on the methods and items of seismic capability appraisement, based on the investigation and analysis on earthquake damages of masonry structure buildings.Safety appraisement of buildings damaged in the disaster mainly include: earthquake damages inspection and analysis, safety inspection, seismic appraisement and reliability appraisement. In our paper, referring to appraisement of a commercial-residential with typical earthquake damages, studies were carried out on the of safety inspection method, seismic appraisement process of masonry structure buildings based on the investigation and analysis of its earthquake damages; also, the strengthening technology was discussed.Commercial-Residential Building (No.2-C) of Knitting Mill in Jiannan town, Mianzhu city, a primer-frame masonry structure with 5 storeys (6 storeys partially) designed in 1999, was appraised into degrade C (moderate damaged) in Emergency Appraisement. Figturel shows the structural Plan of this building.2. INSPECTION AND ANALYSIS ON EARTHQUAKE DAMAGESDifferent from the appraisement of normal buildings, appraisement of damage buildings in earthquake-stricken areas must take earthquake damages and their effects on seismic capability and reliability into consideration. So, the buildings earthquake damages were inspected and analyzed before appraisement, and damage of the mass structure was classified into four levels: severe, moderate, slight damage and basically sound.Earthquake damages of foundation can be reflected by cracks on walls caused by uneven settlement, variation of the surrounding floor, incline of upper structure and their variation tendency. So, appraise foundations damage grades can be appraised by inspecting on items mentioned above.Fig.1 Ground plan of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city(a) Ground Plan, and (b) Standard PlanDamage inspection of masonry structure building should focus on the following locations: four corners of the building, walls on the ground floor, walls of big room, load bearing walls, ring beams, structural columns, connection of walls, and so on.For example, we detected earthquake damages of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city, and summarized as followings:(1) Uplift or depression of ground surrounding the building, cracks and difference of elevation between walls and its surrounding ground, disruption and depression of floor (the biggest depression measured is 68.9mm), differential settlement of mass structure (the difference of elevation measured at sides of expansion joint is 20.9mm) (Fig.2.a).(2) Horizontal shear failure or concrete crisped at the column capital on the ground floor (Fig.2.b).(3) Varying degree of incline, X-shaped, horizontal and vertical cracks on walls: severely cracked, distorted or even partial collapsed of outer longitudinal walls; and damages were severer from the top down.(4) No severe damages on ring beams or structural columns.(5) Obvious cracks along a few precast concrete panel joint (Fig.2.f).(7) Severe cracks on longitudinal walls on the ground floor of stair hall, vertical cracks on the string pieces (in the middle often), severe cracks on the parapet wall at the corner.Fig.2 show damages of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city. Considering severe cracks on much more walls and obvious cracks of corners of longitudinal and cross walls, we appraised the damaged grade of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city into moderate damage.Fig.2 Damages of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city(a) Disruption and Depression of Floor Tiles in the Shops Doors. (b) Horizontal Shear Failure at the Column Capital. (c) X-Shaped Cracks on Walls under Windows. (d) Horizontal Cracks on Bearing Cross Walls. (e) Incline Cracks Along Corners of Opening for Doors, and (f) Horizontal Cracks Along A Few Precast Concrete Panel JointFrom the investigation of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city and other masonry structure buildings, it can be conclude that the earthquake damages of masonry structure building mainly represented as follows.(1) Uplift or depression of ground surrounding, cracks and difference of elevation between walls and its surrounding ground can be found, when the building located in the field bad geological condition.(2) Severely destroyed of the mass structure; and damages of masonry structure were mostly centralized at the bottom 23 layers of buildings, four corners and the ground floor of building particularly. Also, partial collapsed walls can be found on the ground floor.(3) Most earthquake damages of masonry structure building were cracks on walls: the most common damages were X-shaped cracks on walls under or between windows (outer longitudinal) (Fig.2.c) and incline cracks corners along corners opening for doors or windows (Fig.2.e); then X-shaped, incline cracks on load bearing cross walls and inner longitudinal walls, also few horizontal and vertical cracks can be found (Fig.2.d).(4) Cracks were easily produced on cross walls at the connection of walls.(5) Played their roles of tying walls up, seldom ring beams and structural columns were severely destroyed.(6) Horizontal cracks along a few precast concrete panel joint can be found because of bad concreteness led by using of precast concrete slab.(7) Damages were severer from the top down.(8) Designed and built according technical code strictly, buildings newly built performed more excellently than the past which may had not been designed at all.3. SAFETY INSPECTIONConsidering the demand of seismic capability and reliability appraisement, the inspections were primarily carried out on structural measures of whole structure and materials strength. The inspection contents can be interpreted from inspection of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city following: (1) The building used primer-frame masonry structure and precast concrete panels, and it used cross walls to bear load. The U-shaped plane from was cut into two rectangle by expansion joint, so the structure plane from can be considered as two rectangles.(2) Five storeys altogether (six storeys partially) and 3m high for each storey, the building is 16.2m high (eaves height, 19.2m partially). (3) Its load-bearing walls (cross walls) were masonry by fired common bricks (240mm), and the maximum space between windows and other partial dimensions can satisfy the requirement of technical code.(4) The strength of mortar for brick inspected can not satisfy the demand of design, which is M7.5 (the first and second floor) and M5 (other floors). And the strength of bricks designed was MU10.(5) Structural columns were erected at corners of outer walls, once every other intersection of cross walls and outer walls, each corner of stairwell, and both sides of big openings for doors or windows. Ring beams were erected every floor. The sectional dimension and ring beams are both 240*240mm2/412. The Compressive strength of Structural columns and Ring beams can satisfy the demand of design.(6) 26 tie bats were assembled every 500mm from top to bottom of walls.(7) The maximum displacement of mass structure was 8.6mm, while the maximum storey displacement was 5.2mm.(8) The damages of ring beams and structural columns were not so obvious. But damages on seismic cross walls and connections of walls were found which affect the seismic capacity and reliability of buildings.4. SEISMIC APPRAISEMENTWhen we appraised buildings damaged in Wenchuan Earthquake, we should follow the provisions of Technical guidelines for appraisement and strengthening of building after earthquake (2008132 by MOHURD) and technical specification for seismic appraisement and strengthening of building in Sichuan province (DB51/D5059-2008). The appraisement process of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city is as followings:(1) Though uplift or depression of ground surrounding, but the incline of upper structure was not so serious (maximum displacement of mass structure was 8.6mm) and there was no evidence of development. All of these indicate that it has no serious static defect and can satisfy the requirements of seismic appraisement.(2) The structure system, plan and elevation form, maximum height of storey and mass structure, maximum number of layers, maximum space between cross walls, partial dimensions (maximum width of walls between opening for doors or windows), erection of ring beams and structural columns, and fastenings and connections of accessory and main structure all can satisfy the requirements of seismic appraisement.(3) Affecting the seismic capacity of walls and mass structure, available seismic capacity of several seismic cross walls severe cracked and connections of walls slacked can not satisfy the requirements of seismic appraisement. Available seismic capacity of other walls not cracked can satisfy the requirements of seismic appraisement.(4) According to items appraised above and DB51/D5059-2008, it can be appraised that the available compound seismic capacity of the building can not satisfy the requirements of seismic appraisement considering its performance in the earthquake. But as it experienced the massive earthquake in Wenchuan and met the demand of “not collapse when macro-quake happens”, the building has its value to be strengthened.By referring to seismic appraisement of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city and others, seismic appraisement methods can be concluded. In seismic appraisement, the compound seismic capacity of the mass structure should be appraised according to walls available capacity and the results of the first level seismic appraisement, in which macro-control and details of seismic design were mainly appraised; also, its real performance in the earthquake should be taken into consideration. Actually, the appraisal principle above conformed to the technical specification DB51/D5059-2008.Determination of walls available capacity is the most important process in seismic appraisement of building. Walls available seismic capacity can be determined mainly referring to its performance and damage level in the earthquake. It can be considered that walls lost most of their bearing capacity and had very poor available seismic capability when severe damages (oversized cracks) were found on them. But available seismic capability of walls with few damages should be determined by their damages, strength of brick and mortar, and so on.Items of the first level seismic appraisement could be appraised by simple calculation or directly compared to standards.5. RELIABILITY APPRAISEMENTBased on its earthquake damages and the results of seismic appraisement buildings reliability was appraised according to Standard for appraiser of reliability of civil buildings (GB50292-1999).Considering the damage characteristics, the reliability of masonry structure building was appraised mainly according to the earthquake effects to its safety and usability. For example, safety appraisement of wall members was mainly referred to their crack grades and damages at the connection. But mass structure was appraised at a macroscopic level, taking damage grade and position, seismic concept design, details of seismic design of mass structure into consideration. The appraisement concept can be interpreted from the appraisement process of Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city following: (1) Dividing the building into three levels: member sub-system, and appraisement system.(2) Considering it has no serious static defect, but slight differential settlements, the safety of building foundation (sub-system) was appraised as degrade Bu, usability degrade Bs and reliability degrade B.(3) Because of their poor available capacity cause by severely cracks, the safety of most wall members on the ground and first floors were appraised as degrade Cu, but most wall members on the above floors were appraised as degrade Bu. Safety of superstructure (sub-system) can be appraised as degrade Cu, usability degrade Cs (because damages effect on usability was so obvious) and reliability degrade C.(4) The safety of accessory structure (sub-system) can be appraised as degrade Bu, usability degrade Bs and reliability degrade B, because of damages of stairwell and other accessory structures.(5) According to items appraised above and GB50292-1999,it was appraised that safety degrade of the building is Dsu, usability Css and reliability , taking its performance in the earthquake in to consideration. The bearing capacity and usability of the building was severely affected by earthquake, and should be enhanced.6. REPAIR AND STRENGTHENING TECHNOLOGYStrengthened value should be evaluated before design: because of severe cracks on walls or even partial collapse and not so high quality of design and construction, there are poor strengthening values for severely destroyed buildings; but high strengthened value for moderate damaged ones, as they experienced the massive earthquake in Wenchuan and (or even exceed) the demand of “not collapse when macro-quake happens”.When strengthening a building damaged in earthquake, member must be separated into be repaired or strengthening according to their available bearing capacity, taking economic consideration and beautiful appearance should into consideration. Following the principle that pay equal attention to repair, strengthening and long-term maintenance, strengthening should radically improve the aspects which are to the according to damage reasons and results of inspection and appraisement.The suggestions for Commercial-Residential Building (NO.2-C) of Knitting Mill in Jiannan town, Mianzhu city are as following:(1) There is high strengthening value of the building, as it experienced the massive earthquake in Wenchuan and met the demand of “not collapse when macro-quake happens” because of its comprehensive details of seismic design for mass structure.(2) Rebuilding walls severely destroyed, such as longitudinal walls on the bottom two floors of stair-hall. Using masonry strengthening with piaster splity or concrete splity on both sides of walls to strengthening walls which were severely cracked (or over sized cracks were found), after cracks pointed and repaired with polymer mortar. And for members who can satisfy the demand of safety but usability, only repairing measures such as surface retrowelling and crack pouring are OK.(3) Casting a concrete layer (about 50mm) on the precast concrete slab or erect steel tie bar under the slab, to enhance its monolith.From the suggestion it can be conclude that structural measures of mass structure and strength