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The reliability of building structure design

Author: WangYing From: www.yourpaper.net Posted: 2010-06-24 02:42:57 Read:
Abstract: building structure as a special commodity, to determine the design reliability level should not be pure government behavior, at least should be housing developers, the insurance industry and user participation.Low reliability principle the structure design of our country has already cannot adapt to the current situation of our country, improve the structural design of the reliability level will be conducive to the production, living standards improve, conducive to the development of national economy, also accord with the interests and demands of building owners.
Keywords: building structure design; reliability; design method; improvement measures; practical method of
Structure design of reliability of choice, not only relates to the loss of life and property, sometimes have a bad influence in society will also, on some structure, is likely to have serious political consequences; but also related to national economic and technical and economic policies.
Reliability design method of
A, the current structure
The reliability of structure means within the prescribed time, under specified conditions, the probability of expected function, namely the structural reliability is a measure of the probability of structural reliability.Analysis of structure reliability is to reasonably determine the structure reliability level, make the structure design with advanced technology, reasonable economy, safety and quality requirements.
Structure design of China's earliest established norms exist many defects in the safety degree.If the use of reliability index cutter unified analysis, will find that the main problem is the specification and the same specifications of each structural member, even the same component in different conditions safety level are not consistent.
Our previous "standard" architectural structure design of GBJ68-84, to analyze the original specification of the safety level in accordance with the calibration method, and determine the safety level of the new specification.By using reliability design method, you must select a target reliability index is new, the index should be more reasonable, but not deviate from the original specification is too far."Standard" GBJ68-84 is essentially the inheritance of our original specification of building structure safety degree level.Analysis results show that, the original specification of the safety level is acceptable in general, but for some high or low, and make appropriate adjustments, in order to make various kinds of structural members to achieve more consistent reliability levels.
The Ministry of construction in 2001 launched a new building structure "unified standard for reliability design of" GB50068-2001, the latest version of the standard reference to international standard 1SO2394 "structural reliability principle", design different types of building structure service life is given; in the design expression of the limit state of bearing capacity, the basic combination of loads effect, increase the permanent load effect plays a role of controlling the combined; the floor live value principle and structure component load, wind load, snow load standard value of reliability index and structure importance coefficient to do the adjustment; reliability is also the first time for members in serviceability limit state under the provisions.
The new "unified standard for reliability design of building structures" to the original "uniform standard" made a big correction, but in the current structure design method still exist deficiencies, mainly in the following aspects.
1, the design service life of only considering several specific, such as 50 and 100 years, can not fully reflect the different buildings on the needs of different design working life.And in GB50068-2001, change service life design is through the structure importance coefficient 0 to consider, when the design service life is increased, increasing the importance factor of structure.But the design service life increasing, constant load and has not changed, and the importance of coefficient increases to also increase the effect of dead load, the bigger discrepancy exists with the actual situation.
A value of 2, the importance factor of structure is too simple.For all types of component force, as well as all the loads, the importance coefficient of only several fixed value, respectively 0.9, 1, 1.1.Doing so will make some calculations are somewhat conservative, and some significant safety problems.Should be based on the actual situation, in accordance with the different stress and load types are determined.
3, design expression defects, may lead to unreasonable results.
Reliability design of the improvement of
two, the current structure
Aiming at the shortcomings of the existing design methods, this paper presents an improved method on the current design method.Firstly, the effects of different design working life to consider changes in the partial coefficient of variable loads, with implicit existing standards of structure in the design of reliability index for 50 years, to determine the variable load factor structure in other design service life.Secondly, the importance of determining coefficient of different level of security structure in different design working life.According to the above objectives, proposed the improvement design of structure
Gamma 0 ( GSGK Q LSQK) R ( R, ? K, aK,...
Improved design of expression embodied in the gamma 0, gamma two L coefficients.Coefficient 0 or on behalf of the structure importance, for the entire load effect combination value.For different design working life, has different importance coefficient.Gamma L is variable load factor structure of different design working life, only for the variable load value, used to consider the effect of variable load at different design working life.
Gamma 0, gamma L value determination principle is when the same security level, consistent with the reliability level according to different design service life of the designed structure; and when the design service life of 50 years, implied by its reliability level and the current design code for reliability levels consistent.Expression of design expression is improved in the form and the current "standard" provisions are similar, just add a partial coefficient L.When the design of different age structure, only need to determine the corresponding L, so for the use of the engineering design personnel will not cause trouble.
Determined in different design working life of the subentry coefficient L and importance coefficient 0, first need to determine implied the design code structure reliability level, and taking it as the target reliability index.Since the current design specification has adjusted the load value principle and resistance partial coefficient, therefore in the reliability index to determine the implied by the current design code for, also made the corresponding adjustment.
Reliable and practical method of design of
three, building structure
Considering the effect of reinforcement corrosion on the resistance of the concrete structure, based on the reliability design specification design principle of the current structure, reinforced concrete building structure reliability design for expected service life can adopt practical methods are as follows:
1, according to the structure features, as well as the importance of the owners demand, based on design stage, consider the durability of structure reliability influence, put forward the concept of using reliability design expectations of reinforced concrete structure.Structure of expected quantitative index difference load level of durability life reliability design should consider the different environment may cause degradation, different expected service life and is expected to use a resistance period structure degradation.
2, based on the reliability design theory of our country standard, put forward in a given environment, different expected service life of structural reliability principle, practical method of reinforced concrete structure reliability design for expected service life are given.The method boils down to is expected in the period of use of structural reliability index cannot be lower than the current standard, the requirements of concrete through quantitative consideration of the member in the period of use of resistance degradation, improve the initial reliability index is achieved, then according to the current design method into water durability reduction coefficient (or resistance reduction factor) load and resistance factor design expression.The method is simple, easy to master and implement design personnel.
3, for the reinforced concrete members five representative, different expected service life durability design parameters is presented, including the representation of the component reliability index changes with the use of attenuation, consider the durability of the different expected service life design reliability index and the practical design expression reduction coefficient.Through the design of reinforced concrete examples demonstrate the effectiveness of the proposed method, compared with 50 and 100 years of expected service life under considering and not considering the influence the durability of reinforcement, the initial reliability index and reliability index are expected to use the final.
4, for the conditions of architectural environment where moist, rebar corrosion has remarkable effect on the shear component reliability, durability degradation factors must be taken into account; the axial tension, axial compression, large eccentric compression and bending members, reliability index changes of less use of a period of 50 years, the design can not consider degradation effect of durability; but with the increasing of expected service life, should consider the impact of durability, and recommended by this method in the design consideration.
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