外文资料：
Prestressed Concrete Buildings
Prestressed concrete has been widely and successfully applied to building construction of all types.Both precast pretensioned members and cast-tensioned structures are extensively employed,sometimes in competition with one another, most effectively in combination wit each other.
Prestressed concrete offers great advantages for incorporation in a total
aspects of these, that is, structure plus other building. It is perhaps the “integrative”
functions,which have made possible the present growth in use of prestressed concrete buildings.These advantages include the following:Structural strength; Structure rigidity;Durability;Mold ability,into desired forms and shapes;Fire resistance;Architectural treatment of surfaces;Sound insulation;Heat insulation; Economy; Availability, through use of local materials and labor to a high degree.
Most of the above are also properties of conventionally reinforced concrete. Presrressing,however,makes the structural system more effective by enabling elimination of the technical of ,cracks that spoil the architectural treatment.Prestressing greatly enhance the structure eff
iciency and economy permitting longer spans and thinner elements.Above all,it gives to the architect-engineer a freedom for variation and an ability to control behavior under service conditions.
Although prestressed concrete construction involves essentially the same consideration and practices as for all structures, a number of special points require emphasis or elaboration.
The construction engineer is involved in design only to a limited extent. First,
he muse be able to furnish advice to the architect and engineer on what can he done. Because of his specialized knowledge of techniques relating to prestressed concrete construction, he supplies a very needed service to the architect-engineer.
Second, the construction engineer may be made contractually responsible for the working drawings;that is,the layout of tendons,anchorage details,etc.It is particularly important that he gives careful attention to the mild steel and concrete details to ensure these are compatible with his presressing details.
Third, the construction engineer is concerned with temporary stresses, stresses at release, stresses in picking, handling and erection, and temporary condition prior to final completion of the structure, such as the need of propping for a composite pour.
Fourth,although the responsibility for design rests with the design engineer, nevertheless the construction engineer is also vitally concerned that the structure be successful form the point of view of structural integrity and service behavior. Therefore he will want to look at the bearing and connection details, camber, creep, shrinkage,thermal movements,durability provisions,etc.,and advise the design engineer of any deficiencies he encounters.
Information on new techniques and especially application of prestressing to buildings are extensively available in the current technical literature of national and international societies.The International Federation of Prestressing(I.F.P)has attempted to facilitate the dissemination of this information by establishing a Literature Exchange Service,in which the prestressing journals of some thirty countries are regularly exchanged.In addition,an Abstract is published intermittently by I.F.P The Prestressed Concrete Institute(USA)regularly publishes a number of journals and pamphlets on techniques and applications, and procedures
are set up for their dissemination to architects and engineers as well as directly to the construction engineer. It is important that he keep abreast of these national and worldwide developments, so as to be able to recommend the latest and best that is available in the art,and to encourage the engineer to make the fullest and most effective use of prestressed concrete in their buildings.
With regard to working drawings, the construction engineer must endeavor to translate the design requirements into the most practicable and economical details of accomplishment,in such a way that the completed element or structure fully complies with the design requirement;for example, the design may indicate only the center of gravity of prestressing and the effective prestress force. The working drawing will have to translate this into tendons having finite physical properties and dimensions.If the center of gravity of pre-stressing is a parabolic path then,for pre-tensioning,and approximation by chords is required,with hold-down points suitably located.
The computation of pre-stress losses,form transfer stress to effective stress, must reflect the actual manufacturing and construction process used,as well as thorough knowledge of the properties of the particular aggregates and concrete mix to be employed.
With post-tensioning, anchorages and their bearing plates must be laid out in their physical dimension. It is useful in the preparation of complex anchorage detail layouts to use full-scale drawings, so as to better appreciate the congestion of mild steel and anchorages at the end of the member. Tendons and reinforcing bars should be shown in full size rather than as dotted lines. This will permit consideration to be given as to how the concrete can be placed and consolidated.
The end zone of both pre-tensioned and post-tensioned concrete members
subject to high transverse or bursting stresses. These stresses are also influenced by minor concrete details,such as chamfers.Provision of a grid of small bars (sometimes heavy wire mesh is used), as close to the end of a girder as possible, will help to confine and distribute the concentrated forces. Closely spaced stirrups and/or tightly spaced spiral are usually needed at the end of heavily stressed members.Recent tests have confirmed that closeness of spacing is much more effective than increase in the size of bars. Numerous small bars, closely spaced, are thus the best solution.
Additional mild-steel stirrups may also be required at hold-down points to resist the shear. This is also true wherever post-tensioned tendons make sharp bends. Practical consideration of concretion dictates the spacing of tendons and ducts. The general rules are that the clear spacing small be one-and-one-half times the maximum size of coarse aggregate. In the overall section, provision must be made for the vibrator stinger.Thus pre-stressing tendons must either be spaced apart in the horizontal plane, or, in special cases, bundled.
In the vertical plane close contact between tendons is quite common.With post-tensioned ducts,however,in intimate vertical contact,careful consideration has to be given to prevent one tendon form squeezing into the adjacent duct during stressing.This depends on the size of duct and the material used for the duct.A full-scale layout of this critical cross section should be made.Usually,the be
st solution is to increase the thickness ( and transverse strength ) of the duct, so that it will span between the supporting shoulders of concrete.
As a last rest\ort it may be necessary to stress and grout one duct before stressing the adjacent one.This is time-consuming and runs the risks of grout blockage due to leaks from one duct to the other. Therefore the author recommends
the use of heavier duct material,or else the respacing of the ducts.The latter,of course, may increase the prestressing force required.
中文翻译：
预应力混凝土建筑
预应力混凝土已经广泛并成功地用于各种类型的建筑。无论预制先拉构件，还是现浇后张构件都已大量应用，在应用二者时会相互竞争，但结合应用效率更高。在react to stress的中文翻译
预应力混凝土为一栋建筑物的总体结合提供了方便。或许正是因为其在建筑结构及其他功能结合上所起的作用，才使得预应力混凝土应用得以推广。其优点体系在下述各项；结构强度；结构港督；耐久性；可塑性，可制成所需求的方式和形状；抗火性；表面的建筑处理；隔声；绝热；经济性；可行性，可通
过使用本地原料和劳动力达到较高的程度。
上面大都是传统钢筋混凝土具有的特点。然而，预应力通过对建筑有破坏作用的裂缝等缺陷源的消除，而使结构系统更加有效。由于允许采用较长和较薄构件，预应力大大提高了结构的效率和经济性。更重要的是，它为建筑师提供了一种变化的自由，以及在各种服务条件下的行为控制能力。
尽管预应力混凝土结构在本质上有着和所有结构一样的设计考虑和操作，但应重视和推敲一下特殊点。
施工工程师在设计中参与的工作是有限的。首先，他必须能够向建筑师和工程师提供可行性的建议。由于其具有预应力混凝土施工方面的专业技术知识，他将为建筑师和工程师提供非常必要的服务。
其次，施工工程师应通晓施工图。例如钢筋的放置及锚定细节的等。尤为重要的是他应对钢筋和混凝土细节给予足够重视，以使其能够与预应力细节相一致。
第三，施工工程师应该在结构完工之前，注重钢筋的临时应力、松弛应

版权声明：本站内容均来自互联网，仅供演示用，请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系QQ:729038198，我们将在24小时内删除。