Stiffness of composite sections
In structural elements in which there is concrete in compression, the effective equivalent steel section is calculated assuming that the concrete in compression is uncracked. This is reflected in the value for the modular ratio n EJEcm 7. In structural elements in which the concrete is in tension, the effective equivalent steel section is calculated neglecting the concrete in tension and considering only the reinforcement. As a result, the stiffness of the section can be different, depending on...
Simplified design of frames with decoupled diagonal bracings
The structural behaviour of decoupled diagonal bracings is similar to that of X bracings, but as there are two braced zones, each containing one diagonal instead of two, the problem of overstrength described above for X bracings takes place differently, as twice as many columns are involved in the bracing. For this reason, clause 6.7.3 2 states that no lower bound value of slenderness restricts the possible dimensions of the diagonals in this case. However, to be complete the design must also...
Systems of large lightly reinforced walls
Eurocode 8 is unique among international codes in that it includes special provisions for systems consisting of a fairly large number of large but lightly reinforced concrete walls which are designed to sustain seismic demands not by dissipating kinetic energy through hysteresis in plastic hinges but by converting part of this energy into potential energy of the masses and returning part to the ground through radiation from their foundation. To qualify for the special design provisions of...
Verification for the nolocalcollapse requirement
What was said in Section 2.2.2.1 concerning seismic design for energy dissipation normally through ductility with a q factor greater than 1.5, and in Section 2.2.2.2 on design without energy dissipation or ductility and with a q factor not greater than 1.5 for overstrength, applies to buildings. The specific rules for the fulfilment of the no- local -collapse requirement within the framework of design for energy dissipation and ductility are elaborated further here. 4.11.2.1. Verification in...
Nondissipative composite columns
The majority of column members are non-dissipative, because the intended global dissipative mechanisms of structures involve as little energy dissipation in columns as possible. For this reason, only their elastic response needs to be assured, which is done essentially by complying to Eurocode 4. There are, however, differences between a standard design to Eurocode 4 and the earthquake context. The origin of the first difference is in the 'cyclic' aspect of the response, which can degrade the...
Analysis of frames with concentric bracings considering their evolutive
Clauses 6.7.1 1 , In Eurocode 8, the design concept for frames with concentric bracings is that diagonals in 6.7.2 2 tension are the reliable dissipative zones, while diagonals in compression buckle and do not contribute significantly to stiffness and resistance. The problem is that the reality is evolutive. In a first stage, the compression action effect in the diagonal can increase up to the buckling strength ,Npl Rd however, in the following cycles the strength of that diagonal in...
Large lightly reinforced walls
Walls with a large horizontal dimension compared with their height cannot be designed effectively for energy dissipation through plastic hinging at the base, as they cannot be easily fixed there against rotation relative to the rest of the structural system. Design of such a wall for plastic hinging at the base is even more difficult if the wall is monolithically connected with one or more transverse walls also large enough not to be considered merely as flange s or rib s of the first wall....
Materials
Clause 7.2.1 1 The first requirement in clause 7.2 refers to the strength classification of structural concrete The concrete should correspond to class C25 30 as a minimum C25 30 is a standard value for structural applications in buildings, in particular for slabs. The concrete should correspond to class C40 50 as a maximum the reason behind this restriction is the reduction of the crushing strain ecu with increased concrete strength. In developments of clauses for ductility of beam sections...
Partial strength connections 1
Clauses 6.8.4 2 , Frames with eccentric bracings making use of partial strength connections do not correspond 6.8.4 3 to the original intention of such bracings, which is to dissipate energy in zones of structural members called 'seismic links'. Nevertheless, using partial strength connections in a topology of frame in which bracings are not concentric is just another way of thinking of the 'link' so there is no real reason against such a choice, once the ductility and stability issues raised...
Limitation of overstrength
As explained in Section 6.2, the complete design process may generate a structure with more strength than strictly needed for the resistance to the design earthquake. The excess in material may have several origins, for example the limits of deflection in the design of beams under gravity loading may lead to sections larger than those needed for resistance to earthquakes the capacity design of columns to meet equation D4.23 . If the design is such that the drift limits under the damage...
Contents
1.1. Scope of Eurocode 8 1 1.2. Scope of Eurocode 8 - Part 1 1 1.3. Scope of Eurocode 8 - Part 5 2 1.4. Use of Eurocode 8 - Parts 1 and 5 with the other Eurocodes 2 1.5. Assumptions - distinction between Principles and Application Rules 3 1.6. Terms and definitions - symbols 3 Chapter 2 Performance requirements and compliance criteria 5 2.1. Performance requirements for new designs in Eurocode 8 and associated seismic hazard levels 5 2.2. Compliance criteria for the performance requirements and...
Ground conditions
The earthquake response of structures is significantly affected by the underlying soil condition. Clause 3.1.1 In this section, general guidelines and requisites for ground conditions are provided. The properties of the ground type at a given site can be characterized through adequate geotechnical investigations, in situ and or in the laboratory. Rules for the identification of ground types are given in a simplified fashion in clause 3.1.1 of EN 1998-1. Guidance for soil investigations and...
Design of dissipative zones
Clauses 6.6.4 2 , As mentioned before, dissipative zones in moment-resisting frames should be plastic hinges 6.6.4 3 , activated by bending moments. They appear at beam ends, due to the shape of the bending 6.6.4 5 , moment diagram under the seismic action see Fig. 6.8 . 6.6.4 6 , Plastic hinges can take place in the connections, in the case of partial-strength or semi-rigid 6.5.5 7 connection design. There are many possible designs, using connecting components of various types flexible end...
Simplified estimation of the effects of accidental eccentricity
Clause The approach outlined in the previous section can also be applied when the lateral force 4.3.3.2.4 1 method is used for the analysis of the response to the two horizontal components of the seismic action. As already pointed out, in the context of the lateral force method this approach is indeed fully consistent with the concept of displacing the masses by the accidental eccentricity with respect to their nominal position. Within the spirit of simplicity normally associated with the...
Special modelling considerations for walls
The marked preference of Section 4.6.1 in favour of member-type modelling, representing Clause every individual structural member between connections to others as a single 3D beam 5.4.3.4.1 4 element, applies also to concrete, masonry or even composite steel-concrete walls, or at least to parts of such walls between successive floors and or substantial openings. Such modelling of walls is often called 'wide-column analogy'. Supporting this position is the requirement of Section 5 of EN 1998-1...
Wall systems
According to Section 5, a system in which, according to the results of the analysis, 65 of the seismic base shear is or rather should be resisted by primary seismic walls is termed a wall system. Wall systems resist the overturning moment directly, through bending moments rather than through axial forces in the individual walls. Provided that they comprise walls fixed at the base and with sufficient stiffness and strength relative to the beams to behave as vertical cantilevers, wall systems...
Special requirements for the design of secondary seismic elements
Secondary seismic elements do not need to conform to the rules and requirements given in Sections 5-9 of EN 1998-1 for the design and detailing of structural elements for earthquake resistance based on energy dissipation and ductility they only need to satisfy the rules of the other Eurocodes 2 to 6 , plus the special requirement of Eurocode 8 that they maintain support of gravity loads when subjected to the most adverse displacements and deformations induced in them in the seismic design...
Scope of Eurocode
Eurocode 8, Design of Structures for Earthquake Resistance, covers, as its title suggests, the EN 1998-1 earthquake-resistant design and construction of buildings and other civil engineering works clauses 1.1.1 1 , in seismic regions. Its stated purpose is to protect human life and property in the event of I.I.I 2 , earthquakes and to ensure that structures which are important for civil protection remain 1.1.1 4 , Eurocode 8 has six parts, listed in Table 1.1. Among them, only Parts 1 EN...
Invertedpendulum systems
An inverted pendulum is defined as a system with at least 50 of the total mass in the upper third of the height, or with energy dissipation at the base of a single element. Literally, one-storey concrete buildings normally fall in that category. Nonetheless, one-storey frames with the tops of columns connected through beams in the two main directions of the building in plan are explicitly excluded from the category, provided that in the seismic design situation the maximum value of the...
Composite columns considered as steel columns in the model used for analysis
Clauses 7.5.3 3 , If a composite column is considered as a steel column in the structural model, it is 7.5.3 4 , a dissipative member, but with only the resistance of the steel parts considered in the 7.6.1 7 dissipative zones. The advantage of this option is that all requirements in Section 7 of EN 1998-1 for composite columns can be ignored. However, the general requirement in clause 7.5.3 4 still applies the capacity design of connections or of the foundation of that column has to based on...
Simplified design of frames with V bracings
The simplified design approach for V or A bracings called inverted V in Eurocode 8 and 'chevron' bracings in North American terminology is different from that considered for X bracings, due to the fact that both the tension and the compression diagonals are considered Clauses 6.7.2 1 , 6.7.4 1 , 6.7.3 1 , 6.7.3 2 , 6.7.3 3 , 6.7.3 4 in the analysis. This results in higher computed stiffness and strength of the structure with respect to an analysis ignoring the compression diagonal. This more...
Degree of composite character
Any steel structure mixed with certain concrete structural components, such as concrete floors or walls, may be defined as a composite steel-concrete structure, since these materials interact to a certain extent. This interaction may be Limited to the resistance to gravity loads or fire. The advantage of this option is that no seismic detailing is required the structure behaves like a steel structure, and is analysed as such. However, the analysis of the structure should correspond to its real...
Special rules for concrete systems with masonry or concrete infills
Section 4 of EN 1998-1 contains special rules for the analysis and design of frame or frame-equivalent concrete buildings and of unbraced steel or composite buildings with non-engineered masonry infills see Section 4.12 of this guide . These rules are mandatory only for buildings designed for DCH. If the building is designed for DCM or DCL, the rules of Section 4 are considered to serve only as a guide to good practice. Section 5 contains additional rules for concrete buildings with infills,...
Design against the adverse effects of pianwise irregular infills
An unsymmetric distribution of the infills in plan may causc torsional response to the translational horizontal components of the seismic action. Obviously, due to the torsional component of the response, structural members on the side of the plan which has fewer infills termed the 'flexible' side in torsionally unbalanced structures will be subjected to larger deformation demands than those on the opposite, heavier infilled side. Analytical and experimental research59'60 has shown that the...
Uniformity symmetry and redundancy
Uniformity, symmetry and redundancy are related characteristics which are normally correlated to structural simplicity The advantage of structural uniformity in the seismic design context is that it allows the inertial forces created in the distributed masses of the building to be transmitted via short and direct paths, avoiding longer or indirect paths. Structural uniformity of the building should be sought both in plan and in elevation. To achieve plan uniformity and symmetry , it may be...
Verification of beamcolumn joints in shear
Clauses Assuming that bond strength along the beam and column bars framing the joint core is 5.5.3.3 I , sufficient to transfer into the joint the full shear force demand, given by equation D5.20 in 5.5.3.3 2 , terms of the horizontal shear force, Vjhd, the body of the joint then resists that shear. This 5.5.3.3 3 shear force is translated into a shear stress, considered uniform within the joint volume, defined by the horizontal distance between the extreme layers of column reinforcement, h-,...
Boundary elements at section ends in the critical region of ductile walls
As noted in the definition of walls in Section 5.2.2, what mainly differentiates the design and Clauses detailing of a wall as a concrete member from that of a column is that for a wall, flexural 5.4.3.4.2 6 , resistance is assigned to the opposite ends of the section flanges, or tension and compression 5.5.3.4.5 6 chords and shear resistance to the web in between. This is accomplished by concentrating the vertical reinforcement and limiting the confinement of the concrete only at the two ends...
I Short links versus long links
Clauses 6.8.2 3 , Seismic links are designed for the computed seismic action effect in shear or in bending of 6.8.2 4 , the link, by complying to 6 8 2 8 ' FEd P,Knk MEd,Mp,link D6.9 6.8.2 9 which Vp_link and Mp Mnk are, respectively, the plastic shear and bending resistance of the K, link fy K d - if Mp gt link fybtl d - Q D6.10 Equation 6.17 in EN 1998-1 allows computation of Vp link taking into account the interaction of shear with axial force, while equation 6.18 in EN 1998-1 allows...
Structural types and behaviour factors
Clauses 6.3.1, The behaviour factor q characterizes the ability of a structure to dissipate energy in plastic 6.3.2 I deformations. A structure can provide high values of q if 9 dissipative zones are able to undergo significant plastic deformations without losing strength 9 the topology of the structure is such that a large number of dissipative zones are activated. The values given in Table 6.2 of EN 1998-1 have been determined in background studies however, there is a direct logic relating...
Design arid detailing roles for timber buildings
This chapter covers the rules for the seismic design of timber buildings, following in a loose Clause 8.1 way Section 8 of EN 1998-1. However, it does not elaborate on all clauses in that section and neither does it strictly follow the sequence of clauses. It is important to stress that for the overall design of a timber building, the rules of EN 1998-1 are additional to those presented in EN 1995-1-1. 8.2. General concepts in earthquake resistant timber buildings Timber is generally considered...
Minimum clamping reinforcement across construction joints in walls of DCH
An additional requirement for DCH walls is to provide across all construction joints clamping reinforcement at a minimum ratio where NEi is the minimum axial force from the analysis in the seismic design situation positive when compressive . Equation D5.50 is derived from the requirement that the combination of cohesion, friction and dowel action at such a joint is not less than the shear stress that may cause shear cracking at a cross-section nearby. According to Eurocode 2, cohesion and...
Accidental eccentricity
When the distributions of stiffness and or mass in plan are unsymmetric, the response to the horizontal components of the seismic action has certain torsional-translational features. These features are sufficiently taken into account in an analysis in 3D for the horizontal components, especially when a modal response spectrum analysis or a non-linear dynamic one is performed. Unlike some other seismic design codes, amplification or de-amplification of the 'natural' eccentricities between the...
Linear analysis for the vertical component of the seismic action
In buildings the vertical component of the seismic action may in general be neglected, because 8 its effects are normally covered by the design for the persistent and transient design situation, which involves the permanent actions dead loads and the imposed ones live loads , both multiplied by partial factors for actions, which are normally significantly greater than 1.0 except when a building has beams with long span and significant mass along the span, the fundamental period of vibration in...
Scope 1
This chapter covers the design of steel buildings for earthquake resistance according to the Clause 6.1.1 provisions of Section 6 of EN 1998-1. It summarizes the important points of Section 6 without repeating them, and provides comments and explanations for their application, as well as background information. The scope of Section 6 covers buildings made of steel frames. However, most of the design conditions defined in Section 6 for materials, connections, types of structures, control, etc.,...
Performance requirements for new designs In Eurocode and associated seismic
As a European standard EN , Part 1 of Eurocode 8 provides for a two-level seismic design Clause 2.1 1 with the following explicit performance objectives No- local- collapse protection of life under a rare seismic action, through prevention of collapse of the structure or its parts and retention of structural integrity and residual load capacity after the event. This implies that the structure is significantly damaged, and may have moderate permanent drifts, but retains its full vertical...
Detailing of the reinforcement
Clauses As stated above, wherever the large wall can resist the design shear force FEd without 5.4.3.5.3 1 , horizontal reinforcement, then it can be constructed without such reinforcement. The 5.4.3.5.3 2 minimum horizontal reinforcement at a recommended amount given in Eurocode 2 for walls subjected to non-seismic actions has to be placed only wherever the wall needs horizontal reinforcement to resist the design shear force. As there is no specific mention of minimum vertical reinforcement in...
S General requirements for nonlinear modelling
Modelling for the purposes of non-linear analysis should be an extension of that used for linear methods, to include the post-elastic behaviour of members beyond their yield strength. Put differently, as a non-linear analysis degenerates into a linear one if member yield strength is not attained during the seismic response, in the linear range of behaviour, modelling for non-linear analysis should be consistent with that used for linear analysis. Consistency does not imply that the level of...
Layout of this guide
All cross-references in this guide to sections, clauses, subclauses, paragraphs, annexes, figures, tables and expressions of EN 1998-1 and EN 1998-5 are in italic type, which is also used where text from EN 1998-1 and EN 1998-5 has been directly reproduced conversely, quotations from other sources, including other Eurocodes, and cross-references to sections, etc., of this guide, are in roman type . Expressions repeated from EN 1998-1 and EN 1998-5 retain their numbering other expressions have...
Favourable factors for local ductility due to the composite character of
The use of composite steel-concrete frames can have positive effects on local ductility these effects are in addition to the phenomena described in Section 6.4 for steel structures Clauses 7.6.1 4 , The positive effect of concrete encasement around steel profiles. Concrete encased in a 7.6.4 8 , profile, or between the flanges of a profile, prevents inward local buckling of steel walls 7.6.4 9 , and reduces strength degradation due to buckling. For this reason, some limits of wall 7.6.4 10 ,...
identification of ground types
Clause 3.1.2 1 The influence of the local soil condition on the seismic response of structures can be quantified by defining ground types with different mechanical properties. Five ground types have been selected to identify the soil profiles. Alphabetical capital letters A, B, C, D and E are used for such profiles. Table 3.1 of EN 1998-1 'ground types1 provides for each ground type a description of the stratigraphic profile and the parameters used to classify the soil. Three parameters have...
Cracked stiffness in concrete and masonry
Clauses 4.3.1 6 , A fundamental assumption underlying the provisions of Eurocode 8 for design for energy 4.3.1 7 dissipation and ductility is that the global inelastic response of a structure to monotonic lateral forces is bilinear, close to elastic-perfectly-plastic. The elastic stiffness used in analysis should correspond to the stiffness of the elastic branch of such a bilinear global force-deformation response. This means that the use of the full elastic stiffness of uncracked concrete or...
Ductile walls coupled and uncoupled
The main type of wall according to Section 5 is the ductile wall, designed and detailed to dissipate energy in a flexural plastic hinge only at the base and to remain elastic throughout the rest of its height, in order to promote - or even force - a beam-sway plastic mechanism for a flexural plastic hinge with high ductility and dissipation capacity to develop at the base, the ductile wall should be fixed there so that relative rotation of its base with respect to the rest of the structural...
I Design and detailing of foundation elements
Foundation elements are normally made of concrete, even when the superstructure may consist of another structural material. Section 5 gives the design and detailing rules which apply to concrete foundation elements footings, tie beams, foundation beams, foundation slabs and walls, piles and pile caps even when the vertical elements founded through them are made of a different material. Section 5 also gives rules for the connection of concrete foundation elements to the vertical ones of the...
Dimensioning for the ULS in bending with axial force
Large walls should be dimensioned for the ULS in flexure without any increase of the design Clauses moments above the base over those obtained from the analysis for the seismic design 5.4.3.5.1 1 , situation. Moreover, the vertical reinforcement placed in the cross-section should be tailored 5.4.3.5.3 3 to the requirements of the ULS in flexure with axial force - e.g. without excess reinforcement and with less minimum web vertical reinforcement than required in ductile walls. The objective is...
Maximum longitudinal reinforcement ratio in the critical regions of beams
Clauses In beams the value of specified via equations D5.ll for plastic hinge regions is provided 5.2.3.4 2 , through an upper limit on the ratio of the tension longitudinal reinforcement in the critical 5.2.3.7 3 a , regions, p, max Asl mJbd. The value of pL max is derived as follows. 5.4.3.1.2 3 , When the tension reinforcement is less than that in compression, A,, lt As2, the ultimate 5.4.3.1.2 4 deformation at the end of the beam will take place when the effective ultimate strain of the...
Partial strength connections
Clause 6.7.3 9 Partial strength connections are not a familiar option in frames with concentric bracings, though several reasons justify the statement that concentric bracings are an excellent application field for such connections. These reasons are 0 Frames with concentric bracings possess a high stiffness because of their topology, and easily fulfil deformation criteria. Thus, unlike moment-resisting frames, additional flexibility in the connections is not penalized by the need to increase...
Design rules aiming at the realization of dissipative zones
Clause 6.2 The following clauses of Eurocode 8 aim at creating conditions for an effective local dissipation of energy based on the principle of capacity design Clause 6.2 defines conditions on material properties such that the yield stress of the different components is under control and the ductile 'weak link' is really a weak link in the chain of resistances. Clause 6.5.5 3 For design in which dissipative zones are intended in the structural elements and not in the connections, a factor of...
introduction and scope
Field experience and analytical and experimental research have demonstrated the overall Clause 2.2.2 6 beneficial effect of masonry infills attached to the structural frame on the seismic performance of buildings, especially when the building structure has little engineered earthquake resistance. If they are effectively confined by the surrounding frame, infill panels reduce, through their in-plane shear stiffness, storey drift demands, increase, through their in-plane shear strength, the...
i Criteria to form a global plastic mechanism
The criteria to form a global plastic mechanism in frames with eccentric bracings are similar Clauses 6.8.3 I , to those with concentric bracings, because they correspond to the same concept 6.8.2 7 1 The beams, columns and connections are capacity designed to the real strength of the seismic links. This is achieved by complying to the following expressions, which are analogous to equation D6.1 NRd MEi, VEd gt 7VEdj q 1.1 lmf2NEdi D6.15 d gt d,G l.l7ov d,E D6.16 2 A criterion gives to each...
Criterion for the formation of a global plastic mechanism
Clauses 6.7.3 5 , The design requirement for diagonals in clause 6.7.3 5 simply expresses the need for a 6.7.4 1 section able to take the computed action effect NFd Npl Rd gt VEd. To form a globally dissipative bracing structure, which means achieving a global plastic mechanism in which yielding affects a significant number of diagonals, two conditions must be fulfilled 1 The beams and columns have to be capacity designed to the real strength of the diagonals. This prevents pre-emptive yielding...