【正文】 用于預(yù)測(cè) 彎曲構(gòu)件中 長(zhǎng)期 變形 及最終裂縫寬度 的 可靠的程序 已經(jīng)被 提 出并 圖例說明 。在使用更高強(qiáng)度鋼筋的構(gòu)件中，那些條文不可能是滿足要求的，因?yàn)樵诂F(xiàn)役荷載作用下的構(gòu)件中的鋼筋應(yīng)力有可能更大，這是因?yàn)闇p少的鋼筋區(qū)域需要足夠強(qiáng)度。 這些限制 值 不依賴 于現(xiàn)役荷載作用下的拉伸鋼筋中應(yīng)力 ， 而且 當(dāng)鋼 筋中 應(yīng)力超過約 240 兆 帕 時(shí) 已被發(fā)現(xiàn)是不可靠的。 在 常規(guī)的 混凝土結(jié)構(gòu) 的可靠性極限狀態(tài)設(shè)計(jì)中 使用 AEMM 是被強(qiáng)烈推薦的 。針對(duì)開裂、拉伸固化、收縮、混凝土的徐變特性以及板的預(yù)期的荷載作用史和雙向作用板，前者應(yīng)該制定的不是細(xì)節(jié)規(guī)定而是個(gè)限定值。撓度的精確 計(jì)算 39。無論是 在 頂部和底部表面 ， 如果干燥條件都是一樣的， 那么 其總應(yīng)變是均勻 沿板的 深 度方向分布，且 等 于板的平均收縮應(yīng)變 ?cs，這是這個(gè) 數(shù)值在在 分析混凝土結(jié)構(gòu)時(shí)的 一般意義。 然而 ，干燥表面附近 的 拉應(yīng)力往往 超過 未成熟混凝土抗拉強(qiáng)度，并造成 表面開裂 ， 在混凝土開始 干燥 后 不久。此板未受荷載和約束。 對(duì)于室內(nèi)環(huán)境， 可取 。 該法應(yīng) 僅限 于 當(dāng) 混凝土 有 低水灰比（ ） ，并具有良好等級(jí)， 骨料的質(zhì)量好 時(shí)的一種參考。 k 1是 由 在標(biāo)準(zhǔn)里的 圖 按照插值法得到的且取決 于干燥 開始的時(shí)間 ，環(huán)境和混凝土表面積及容積率。 干縮在高強(qiáng)度的混凝土 中 小于正常強(qiáng)度的 混凝土， 這是由于水合以后自由水的數(shù)量少的緣故。 因?yàn)樗苄曰炷梁弯摻钪械恼辰Y(jié)還沒有形成，鋼筋 在控制這種裂縫 時(shí)是無效的。 什么是收縮？ 混凝土收縮是 在恒溫下未受荷載且無應(yīng)變的試件上測(cè)量出的時(shí)效性 應(yīng)變 。 在未開裂區(qū)由荷載導(dǎo)致的拉力的存在 加快了時(shí)效性開裂的形成 ， 因此， 在許多情況下，收縮裂縫是不可避免的。 收縮裂縫 的出現(xiàn)取決 于 對(duì)收縮的約束程度、拉伸時(shí)混凝土的強(qiáng)度和延展性以及 拉伸 徐 變和 存在于構(gòu)件中的荷載導(dǎo)致的拉力 。 Electronic Journal of Structural Engineering, 1 ( 2021) 23 （二） 過度 彎曲導(dǎo)致 結(jié)構(gòu)或 與構(gòu)件相聯(lián)系的 非結(jié)構(gòu)性 元素的損害。 2 .可靠性的設(shè)計(jì) 當(dāng)設(shè)計(jì) 可靠性時(shí) ，設(shè)計(jì)者必須確保整個(gè)結(jié)構(gòu)， 在日常荷載的一天天作用下能夠完成它預(yù)期的功能 。 它也必須涉及到 設(shè)計(jì)者更多地重視適當(dāng)?shù)幕炷僚浜媳?的規(guī)定 ，特別是對(duì)于 徐 變和收縮特征的組合， 同時(shí)也要求在建設(shè)過程中有合理的 工程的投入。 無數(shù)的案例報(bào)告 證實(shí) ，在澳大利亞和其他地方 ，結(jié)構(gòu) 符合規(guī)范要求，但仍然 出現(xiàn)過度彎曲和開裂 。 但是 ， 在大多規(guī)范中，簡(jiǎn)化的撓度計(jì)算過程是從鋼筋混凝土簡(jiǎn)支梁的試驗(yàn)中獲得的。 在 許多 實(shí)踐規(guī)范中 ， 明確規(guī)定了在開裂和連接鋼筋達(dá)到允許的最大間距之后鋼筋的最大應(yīng)力 。 其中，收縮是 主要 問題。 混凝土可靠性的設(shè)計(jì)可能是混凝土結(jié)構(gòu)各個(gè)方面中最困難的和最不好理解的 。可靠性 。 關(guān)鍵詞 徐 變 。 Shrinkage. 1. Introduction For a concrete structure to be serviceable, cracking must be controlled and deflections must not be excessive. It must also not vibrate excessively. Concrete shrinkage plays a major role in each of these aspects of the service load behaviour of concrete structures. The design for serviceability is possibility the most difficult and least well understood aspect of the design of concrete structures. Service load behaviour depends primarily on the properties of the concrete and these are often not known reliably at the design stage. Moreover, concrete behaves in a nonlinear and inelastic manner at service loads. The nonlinear behaviour that plicates serviceability calculations is due to cracking, tension stiffening, creep, and shrinkage. Of these, shrinkage is the most problematic. Restraint to shrinkage causes timedependent cracking and gradually reduces the beneficial effects of tension stiffening. It results in a gradual widening of existing cracks and, in flexural members, a significant increase in deflections with time. The control of cracking in a reinforced or prestressed concrete structure is usually achieved by limiting the stress increment in the bonded reinforcement to some appropriately low value and ensuring that the bonded reinforcement is suitably distributed. Many codes of practice specify maximum steel stress increments after cracking and maximum spacing requirements for the bonded reinforcement. However, few existing code procedures, if any, account adequately for the gradual increase in existing crack widths with time, due primarily to shrinkage, or the timedependent development of new cracks resulting from tensile stresses caused by restraint to shrinkage. For deflection control, the structural designer should select maximum deflection limits that are appropriate to the structure and its intended use. The calculated deflection (or camber) must not exceed these limits. Codes of practice give general guidance for both the selection of the maximum deflection limits and the calculation of deflection. However, the simplified procedures for calculating deflection in eJSE International Electronic Journal of Structural Engineering, 1 ( 2021) 16 most codes were developed from tests on simplysupported reinforced concrete beams and often produce grossly inaccurate predictions when applied to more plex structures. Again, the existing code procedures do not provide real guidance on how to adequately model the timedependent effects of creep and shrinkage in deflection calculations. Serviceability failures of concrete structures involving excessive cracking and/or excessive deflection are relatively mon. Numerous cases have been reported, in Australia and elsewhere, of structures that plied with code requirements but still deflected or cracked excessively. In a large majority of these failures, shrinkage of concrete is primarily responsible. Clearly, the serviceability provisions embodied in our codes do not adequately model the inservice behaviour of structures and, in particular, fail to account adequately for shrinkage. The quest for serviceable concrete structures must involve the development of more reliable design procedures. It must also involve designers giving more attention to the specification of an appropriate concrete mix, particularly with regard to the creep and shrinkage characteristics of the mix, and sound engineering input is required in the construction procedures. High performance concrete structures require the specification of high performance concrete (not necessarily high strength concrete, but concrete with relatively low shrinkage, not prone to plastic shrinkage cracking) and a high standard of construction, involving suitably long stripping times, adequate propping, effective curing procedures and rigorous onsite supervision. This paper addresses some of these problems, particularly those related to designing for the effects of shrinkage. It outlines how shrinkage affects the inservice behaviour of structures and what to do about it in design. It also provides an overview of the considerations currently being made by the working group established by Standards Australia to revise the serviceability provisions of AS36001994 [1], particularly those clauses related to shrinkage. 2. Designing for Serviceability When designing for serviceability, the designer must ensure that the structure can perform its intende