即將于2027年9月在歐盟34國(guó)正式執(zhí)行的第二代歐洲結(jié)構(gòu)設(shè)計(jì)標(biāo)準(zhǔn)已于2023年開始陸續(xù)發(fā)布了，第一代歐標(biāo)將于2028年3月30日全部廢止。為方便有關(guān)人員了解第二代歐標(biāo)，現(xiàn)簡(jiǎn)要介紹如下。
第二代歐洲結(jié)構(gòu)設(shè)計(jì)標(biāo)準(zhǔn)由以下10個(gè)部分組成，此外還要新增加有關(guān)玻璃結(jié)構(gòu)設(shè)計(jì)標(biāo)準(zhǔn)。除EN 1990為單一本的標(biāo)準(zhǔn)外，其他部分都由多本子標(biāo)準(zhǔn)構(gòu)成，如EN 1991就由恒荷載、活荷載、風(fēng)作用等9本子標(biāo)準(zhǔn)組成。
—EN 1990 Eurocode - Basis of structural and geotechnical design；（結(jié)構(gòu)與地基設(shè)計(jì)準(zhǔn)則）
— EN 1991 Eurocode 1: Actions on structures; （結(jié)構(gòu)作用）
— EN 1992 Eurocode 2: Design of concrete structures; （混凝土結(jié)構(gòu)設(shè)計(jì)）
— EN 1993 Eurocode 3: Design of steel structures; （鋼結(jié)構(gòu)設(shè)計(jì)）
— EN 1994 Eurocode 4: Design of composite steel and concrete structures; （組合結(jié)構(gòu)設(shè)計(jì)）
— EN 1995 Eurocode 5: Design of timber structures; （木結(jié)構(gòu)設(shè)計(jì)）
— EN 1996 Eurocode 6: Design of masonry structures;（砌體結(jié)構(gòu)設(shè)計(jì)）
— EN 1997 Eurocode 7: Geotechnical design;（地基設(shè)計(jì)）
— EN 1998 Eurocode 8: Design of structures for earthquake resistance; （結(jié)構(gòu)抗震設(shè)計(jì)）
— EN 1999 Eurocode 9: Design of aluminum structures. （鋁結(jié)構(gòu)設(shè)計(jì)）
第二代歐洲結(jié)構(gòu)標(biāo)準(zhǔn)既適用于房屋建筑、一般土木工程如橋梁、地基等的設(shè)計(jì)，也適用于既有建筑的評(píng)估、改造等。
第二代歐標(biāo)的編寫格式及書寫語言與第一代歐標(biāo)相比有很大的變化，采用了shall（應(yīng)）、should（宜）、may（可）、can（可能）等來區(qū)分對(duì)標(biāo)準(zhǔn)條文的不同要求。而第一代歐標(biāo)采用Principles（原則要求，強(qiáng)制性）或Application Rules（應(yīng)用規(guī)定，可選擇性）來區(qū)分強(qiáng)制性和可選擇性，使用起來不很方便。shall、should、may、can的具體定義如下:
The verb "shall" expresses a requirement strictly to be followed and from which no deviation is permit in order to comply with the Eurocodes.
The verb "should" expresses a highly recommended choice or course of action. Subject to national regulation and/or any relevant contractual provisions, alternative approaches could be used/adopted where technically justified.
The verb "may" expresses a course of action permissible within the limits of the Eurocodes.
The verb "can" expresses possibility and capability; it is used for statements of fact and clarification of concepts.
第二代歐標(biāo)規(guī)定設(shè)計(jì)開始時(shí)每個(gè)結(jié)構(gòu)都要按其損壞后對(duì)人的生命危害程度和財(cái)產(chǎn)損失大小劃分為5個(gè)重要性等級(jí)，從最低CC0到最高CC4，EN 1990表A.1.1有各個(gè)等級(jí)的舉例。EN 1990明確規(guī)定本套歐標(biāo)僅適用于CC1、CC2、CC3這三類結(jié)構(gòu)，而CC0（簡(jiǎn)易結(jié)構(gòu)）、CC4(核電站、大壩等)僅可參考使用。
不同重要性等級(jí)結(jié)構(gòu)的可靠指標(biāo)(β)及50年失效概率（Pf.50）見下表：
Table C.3 (NDP) — Target values for reliability index β for different consequence classes (for persistent and transient (fundamental) and fatigue design situations in ULS)
Consequence 重要性等級(jí) | 1-year reference period | 50-yearreference Period（50年） | |
β | Pf.50 | ||
CC3 | 5,2 | 4,3 | ~ 10-5 |
CC2 | 4,7 | 3,8 | ~ 10-4 |
CC1 | 4,2 | 3,3 | ~ 10-3 |
設(shè)計(jì)工況（design situations）是指每個(gè)結(jié)構(gòu)在設(shè)計(jì)使用期內(nèi)可能遇到的各種不同作用組合的情況，第二代歐標(biāo)將設(shè)計(jì)工況分為5類，見下表，不同的工況采用不同的作用組合、不同的作用分項(xiàng)系數(shù)。
Table 5.1 — Classification of design situations（設(shè)計(jì)工況分類）
Design situation
| Conditions | Examples |
Persistent（持久）
| Normal use and exposure | During every day use |
Transient（短暫） | Temporary use and Exposure during a period much shorter than the design service life of the structure | During execution, repair or temporary environmental influence |
Accidental（偶然） | Exceptional conditions or exposure | During flooding, extreme sea water level, fire, explosion, or impact; or local failure |
Seismic（地震） | Exceptional conditions during a seismic event | During an earthquake |
Fatigue（疲勞） | Conditions caused by fatigue actions | Owing to traffic loads on a Bridge，wind induced vibration of chimneys, or machinery- induced vibration |
第二代歐洲結(jié)構(gòu)抗震標(biāo)準(zhǔn)依然與我國(guó)一樣，單獨(dú)編寫，由EN 1998系列組成。EN 1998-1-1（General rules and seismic action）為設(shè)計(jì)原則及地震作用，其他還有5本，分別為：
—EN 1998-1-2 contains specific provisions relevant to buildings; （建筑物抗震設(shè)計(jì)）
—EN 1998-2 contains specific provisions relevant to bridges; （橋梁抗震設(shè)計(jì)）
—EN 1998-3 contains provisions for the seismic assessment and retrofitting of existing buildings and bridges;（既有建筑、橋梁抗震評(píng)估及改造）
—EN 1998-4 contains specific provisions relevant to silos, tanks, pipelines, towers, masts and chimneys;（料倉、儲(chǔ)罐、管線、塔桅、煙囪等抗震設(shè)計(jì)）
—EN 1998-5 contains specific provisions relevant to foundations, retaining structures and geotechnical aspects.（地基及基礎(chǔ)、擋土墻抗震設(shè)計(jì)）
第二代歐標(biāo)抗震部分與原標(biāo)準(zhǔn)有較大變化，設(shè)計(jì)時(shí)根據(jù)不同的需要采用4種不同的地震作用極限狀態(tài)（LS），具體如下：
嚴(yán)重?fù)p壞（SD）極限狀態(tài)：LS of Significant Damage (SD) shall be defined as one in which the structure is significantly damaged, possibly with moderate permanent drifts, but retains its vertical loadbearing capacity; ancillary components, where present, are damaged (e.g. partitions and infills have not yet failed out-of-plane). The structure is expected to be repairable but, in some cases, it may" be uneconomic to repair.
有限損壞（DL）極限狀態(tài)：LS of Damage Limitation (DL) shall be defined as one in which the structure is only slightly damaged and economic to repair, with negligible permanent drifts, undiminished ability to withstand future earthquakes and structural members retaining their full strength with a limited decrease in stiffness; ancillary components, where present, exhibit only minor damage that can be economically repaired (e.g. partitions and infills may show distributed cracking).
正常操作（OP）極限狀態(tài)：Fully Operational LS (OP) shall be defined as one in which the structure is only slightly damaged and economic to repair, allowing continuous operation of systems hosted by the structure.
接近倒塌（NC）極限狀態(tài)：LS of near Collapse (NC) shall be defined as one in which the structure is heavily damaged, with large permanent drifts, but retains its vertical load bearing capacity; most ancillary components where present, have collapsed.
上述的NC與SD屬于承載能力極限狀態(tài)，而DL與OP屬于正常使用極限狀態(tài)。不同的結(jié)構(gòu)根據(jù)其重要性等級(jí)、結(jié)構(gòu)特點(diǎn)等采用不同的極限狀態(tài)。地震作用按不同的極限狀態(tài)、不同的重要性等級(jí)采用不同的重現(xiàn)期，見下表，而OP的重現(xiàn)期可根據(jù)有關(guān)部門或業(yè)主要求確定，無規(guī)定時(shí)也可采用與DL相同的重現(xiàn)期。
Table 4.3 — Return period （重現(xiàn)期，年）TLS.CC values, in years, for buildings
Limit state (極限狀態(tài)) | Consequence class（重要性等級(jí)） | |||
CC1 | CC2 | CC3-a | CC3-b | |
NC | 500 | 1350 | 2500 | 5000 |
SD | 275 | 475 | 700 | 1000 |
DL | 100 | 115 | 125 | 140 |
結(jié)構(gòu)抗震分析可采用力法或位移法，這兩種計(jì)算方法含義如下：
(1) The force-based approach, which employs a linear analysis that implicitly and approximately accounts for the overstrength and the non-linear response through a behavior factor.
(2) The displacement-based approach, which explicitly accounts for the structural non-linear response, may be implemented through a non-linear static analysis.
與美標(biāo)相似，第二代歐標(biāo)在采用線性分析計(jì)算地震作用時(shí)也采用了一個(gè)稱為行為系數(shù)（behaviour factor）的除數(shù)來減小地震作用。行為系數(shù)的定義為：
behaviour factor —factor used for design purposes to reduce the forces obtained from a linear analysis, to account for the overstrength as well as for the non-linear response of a structure, associated with the material, the structural system and the design procedures.
第二代歐標(biāo)地基基礎(chǔ)設(shè)計(jì)由EN 1997系列組成，包括地勘、基礎(chǔ)設(shè)計(jì)、地基處理三部分，分別為：
EN 1997-1, Geotechnical design - Part 1: General rules；（總則）
EN 1997-2, Geotechnical design - Part 2: Ground properties；（場(chǎng)地特性）
EN 1997-3, Geotechnical design - Part 3: Geotechnical structures. （巖土結(jié)構(gòu)物）
其中EN 1997-3的第11章和附錄G專門用于地基處理問題。歐標(biāo)將地基處理方法劃分為兩大類，即整體式處理法（Diffused ground improvement，也稱為面式處理法）和離散式處理法（Discrete ground improvement, 也稱為點(diǎn)式處理法），而每個(gè)類別又劃分為兩個(gè)子類，各子類的定義與做法見下表：
Table 11.1 — Classification of ground improvement(地基處理方法分類)
Class | Family | |
A –Diffused(面式) | B – Discrete（點(diǎn)式） | |
I | AI - Diffused with no unconfined compressive strength The improved ground has an increased shear strength higher than that of the original ground. The improved ground can be modelled as a ground with improved properties. | BI - Discrete with non-rigid inclusions Inclusions, installed in the ground, with higher shear capacity and stiffness compared to the surrounding ground. The unconfined compressive strength of the inclusion is not measurable. |
II | AII - Ground improvement zone with unconfined compressive strength The improved ground is modified from its original natural state, has a measurable unconfined compressive strength and is significantly stiffer than the surrounding ground. Usually, it comprises a composite of a binder and ground. | BII - Discrete with rigid inclusions Rigid inclusions, installed in the ground, with unconfined compressive strength significantly stiffer than the surrounding ground. The inclusions can be an engineered material such as timber, concrete/grout or steel or composite of a binder and ground. |
附錄G 給出了各種處理方法的詳細(xì)描述和執(zhí)行標(biāo)準(zhǔn)，節(jié)選部分內(nèi)容如下：
最后簡(jiǎn)要介紹一下第二代歐標(biāo)關(guān)于結(jié)構(gòu)防火設(shè)計(jì)的有關(guān)內(nèi)容。主要有3本標(biāo)準(zhǔn)與結(jié)構(gòu)防火有關(guān)，它們分別是：
EN 1991-1-2, Actions on structures —Actions on structures exposed to fire;
EN 1992-1-2, Design of concrete structures —Structural fire design ;
EN 1993-1-2, Design of steel structures —Structural fire design.
當(dāng)火災(zāi)發(fā)生時(shí)結(jié)構(gòu)構(gòu)件應(yīng)根據(jù)防火規(guī)范要求必須滿足下列三種功能中的其中一種：
（1）Loadbearing function（承載功能）:loadbearing capacity (R);
（2）Separating function（分隔功能）: integrity(E)（完整性）and, when requested, insulation (I)（隔熱性）;
（3）Separating and loadbearing functions（承載功能和分隔功能）: R, E and, when requested, I.
三種功能具體定義為:
(1) The loadbearing function is assumed to be satisfied when loadbearing capacity is maintained.
(2)The separating function is assumed to be satisfied when integrity and when requested insulation are maintained.
(3) Integrity function is assumed to be maintained when a separating element of building construction, exposed to fire on one side, prevents the passage through it of flames and hot gases and the occurrence of flames on the unexposed side.
(4) Insulation function is assumed to be maintained when the average temperature rise over the whole of the non-exposed surface is limited to 140 K, and the maximum temperature rise at any point of that surface does not exceed 180 K.
耐火極限（fire resistance ）定義為:Ability of a structure, a part of a structure or a member to fulfil its required functions (loadbearing function and/or fire separating function) for a specified load level, for a specified fire exposure and for a specified period of time
上述三種功能（R,E,I）不是所有結(jié)構(gòu)構(gòu)件都要同時(shí)滿足的。每個(gè)結(jié)構(gòu)構(gòu)件在火災(zāi)發(fā)生時(shí)不能失去承載能力（R）,這是最基本的要求。而具有防火分隔功能的結(jié)構(gòu)構(gòu)件還必須同時(shí)要滿足E、I功能，不具有分隔功能的結(jié)構(gòu)構(gòu)件當(dāng)然就不需要E、I功能了。大多結(jié)構(gòu)防火分析程序不具有E和I計(jì)算功能。EN 1993-1-2明確說明其各種分析方法不包括確定E、I功能，這與美標(biāo)AISC 360是一致的。結(jié)構(gòu)工程師要特別注意不是只計(jì)算了某構(gòu)件火災(zāi)時(shí)的承載能力（R）就算完成了結(jié)構(gòu)防火設(shè)計(jì)，而還要考慮此構(gòu)件是否還應(yīng)具有分隔功能（E、I）。另外歐標(biāo)主要考慮兩種火災(zāi)場(chǎng)景：普通火災(zāi)與烴類火災(zāi)。盡管對(duì)這兩類火災(zāi)的耐火極限要求是一樣的，但它們對(duì)結(jié)構(gòu)的作用是不一樣的，烴類火災(zāi)明顯要高于普通火災(zāi)，因此無論是建筑物還是構(gòu)筑物只要火災(zāi)場(chǎng)景是烴類火災(zāi)就要按烴類火災(zāi)進(jìn)行設(shè)計(jì)。歐標(biāo)結(jié)構(gòu)防火設(shè)計(jì)方法主要有實(shí)驗(yàn)法、查表法、簡(jiǎn)化計(jì)算法、先進(jìn)分析法等，設(shè)計(jì)人員可根據(jù)具體情況選擇不同的防火設(shè)計(jì)方法。
第二代歐洲結(jié)構(gòu)設(shè)計(jì)標(biāo)準(zhǔn)代表今后多年歐洲結(jié)構(gòu)設(shè)計(jì)的新方向、新思路、新方法，感興趣的朋友可認(rèn)真學(xué)習(xí)原文，深入了解其內(nèi)容。盡管第二代歐洲結(jié)構(gòu)設(shè)計(jì)標(biāo)準(zhǔn)已經(jīng)正式發(fā)布了相當(dāng)多的部分，但抗震、地基等的最終版還沒有正式公布，本文中有關(guān)這些部分內(nèi)容是按公示稿介紹的，正式版可能有變化，請(qǐng)多關(guān)注。
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