现代预应力混凝土结构应用中两个问题的探讨

对现代预应力混凝土结构应用中存在的、工程界比较关心的两个问题 ,即裂缝控制和抗震设计进行了讨论 ,提出建议 。

体外预应力高强混凝土两跨连续梁模型试验

为研究预应力和混凝土材料对高强度混凝土体外预应力连续梁的力学行为的影响 ,设计并完成了 4片体外预应力高强度混凝土连续梁模型的静载试验。试验结果表明 :体外预应力连续梁的裂缝分布和发展规律与无粘结预应力梁相似 ;采用钢纤维提高负弯矩区的开裂载荷是有效的 ,而且利用钢纤维增强可在一定程度上限制裂缝发展并在卸载后使裂缝闭合 ;普通钢筋对分散裂缝和限制裂缝发展有利。

预应力型钢混凝土组合结构施工技术

近年来,随着中国建筑业的快速发展,建筑工程的类型也逐渐增多.大、高层建筑的快速增长使预应力钢-混凝土组合结构具有自身的特点,并在高层建筑工程中得到了不断的推广和应用.本文对预应力钢-混凝土组合结构的施工特点及应用进行了简要的分析,以供业界共同探讨.

Durability design of prestressed concrete structures

Based on the durability characteristics of prestressed concrete structures,the durability limit states of carbonation and chloride ion attack are defined, respectively.Durability predicting models on the basis of reliability mathematics and stochastic processes areconstructed, and the pure theoretical formulae of failure probability of prestressed concretestructures are analyzed. In addition, a simple durability design method for carbonation ofstructures is put forward. According to the analysis, the durability of prestressed concretestructures is superior to that of traditional structures. The research also indicates that theconcrete cover prescribed in the current code (GB 50010-2002) is not adequate. The rational coverthickness should notbe less than 35 or 45 mm according to carbonation or chloride ion attack,respectively.

Probabilistic Assessment of Pitting Corrosion Effect on Flexural Strength of Partial Prestressed Concrete Structures in a Chloride Environment

Like reinforced concrete （RC） structure, Prestressed concrete （PC） structures cannot escape from corrosion related problems, especially when they are subjected to very aggressive environment, such as chloride environment. The corrosion of PC and RC structures can take place if the concrete quality is not adequate, the concrete cover is less than that specified in the design, poor detailing during design and construction. For RC structures, corrosion in the reinforcing steel generally leads to serviceability problems （staining, cracking and spalling of concrete）. By contrast, for PC structures, corrosion of prestressing strands may initiate structural collapse due to higher stress levels in the steel and smaller diameter of the prestressing steel. Research on corrosion effect on concrete structure has mainly considered the effect of corrosion have on reinforced and full prestressed concrete structure. In this study, a structural framework will be developed to predict the flexural strength of partial prestressed concrete structures in a chloride environment. The corrosion model previously developed for reinforced and prestressed concrete structures will be combined to predict the effect of corrosion has on partial prestressed concrete structures. Note that in partial prestressed concrete structures, both non prestressing steel （passive） and prestressing （active） reinforcement are utilized to carry the load. The framework developed will be combined with probability analysis to take into account the variability of parameters influencing the corrosion process. This approach allows more accurate prediction of service life of partial prestressed concrete structures in a chloride environment.

Durability of Stress Ribbon Bridge Checked during Loading Test

Stress ribbon bridges have many advantages and became recently more popular mostly because of their versatile form, slender decks giving a light aesthetic impression and durability assured by post tensioned concrete. The paper presents the first in Poland stress Ribbon Bridge constructed last year. A static and dynamic analyse of the model is presented as well as construction solutions which were used to achieve the highest durability. The bridge was checked during static and dynamic load test. The results of this prove test were compared with results obtained from examination and study of other different bridge structures. It confirmed that the bridge has good dynamic resistance and greater stiffness than assumed in the design.

Interaction between Engineering Structures and Environment, Illustrated on the Examples of Bridges in Montenegro

The basic goal of this paper is to point out the importance of design shaping as well as the key parameter of the great interaction between the structure and natural environment. However, experiences confirm the fact that the most successful structures, the bridges also, have not got that attribute because of their grandiosity but per their great integration in the nature that is environment. Beside the basic function, that is the usage to man, their integrations in the environment greately enrich the ambience. The old stone bridges are mostly well integrated in the natural environment. In the period of large building, it did not take care of the parameters （the bridges of steel, concrete and prestressed concrete）, but great attention was paid to records referring to spans and complicated forms. The author thinks it is necessary to take care about integration of all building structures in the environment, especially bridges. As a good example of successful creation, simplicity of form, and especially good integration in the natural surroundings are three bridges from Montenegro, one of them is old stone bridge, others are reinforced-concrete and steel bridges.

Degradation process assessment of prestressed concrete continuous bridges in life-cycle

To accurately evaluate the degradation process of prestressed concrete continuous bridges exposed to aggressive environments in life-cycle,a finite element-based approach with respect to the lifetime performance assessment of concrete bridges was proposed.The existing assessment methods were firstly introduced and compared.Some essential mechanics problems involved in the degradation process,such as the deterioration of materials properties,the reduction of sectional areas and the variation of overall structural performance caused by the first two problems,were investigated and solved.A computer program named CBDAS(Concrete Bridge Durability Analysis System) was written to perform the above-metioned approach.Finally,the degradation process of a prestressed concrete continuous bridge under chloride penetration was discussed.The results show that the concrete normal stress for serviceability limit state exceeds the threshold value after 60 a,but the various performance indicators at ultimate limit state are consistently in the allowable level during service life.Therefore,in the case of prestressed concrete bridges,the serviceability limit state is more possible to have durability problems in life-cycle;however,the performance indicators at ultimate limit state can satisfy the requirements.

Emerging Timber Bridge Program to Sao Paulo State： A Five-Year Report

The Emerging Timber Bridge Program to Sao Paulo state （ETBPSP） was started in 2001 with the main objective of research and development of new technologies for timber bridge construction. After five years of this program eleven demonstration timber bridges were constructed in the State of Sao Paulo, whereas eight composite timber/concrete bridges, one log timber girder bridge with transversal sawn deck, one transversal lumber prestressed timber bridge and one transversal cellular plywood box prestressed bridge. As a final objective is the divulgation of the constructive and structural systems in extension courses to municipal engineers and in a complete publication of timber bridges project plans with the different structural and constructional systems. This paper describes the goals of the MTBPSP, the accomplishments of the program in the first five years, the information sheet of the bridges and outlines some obstacles and opportunities.

旧桥加固设计与施工初探

旧桥由于使用年限较长、竣工资料不全、现有的检测手段又不能准确测定其受力状态.使加固设计的依据不足。本文从桥梁病害的特征出发,通过对病言的模拟分析,拟合其受力状态,作为加固设计的依据。对其进行了有针对性的加固设计。

Study Progress of FRP Rebars in Concrete Structures

Fiber reinforced plastics (i. e. FRP) rebars are one kind of high-performance composite materi- als used in concrete structures of civil engineering. Compared with ordinary steel rebars, FRP rebars have the characteristics of high tensile strength, an- tisepsis, light weight, low elastics modulus and low shear strength, et al. At present time, FRP re- bars have been studied and applied in Europe, America and Japan Since 2000, in the Fund of NS- FC, we systematically carried out experimental and theoretical studies on FRP rebars The progress of our research is briefly introduced in this paper.