ACI 374.1:2005 download free.Acceptance Criteria for Moment Frames Based on Structural Testing and Commentary.
For seismic design, ACI 318-99 specifies in Section 21.2.1.5 that a reinforced concrete structural system not satislying the requirements of this chapter (Chapter 21) shall be pennitted if it is demonstrated by experimental evidence and analysis that the proposed system has strength and toughness equal to or exceeding those provided by a comparable monolithic reinforced concrete structure that satisfies the requirements of this chapter.” This Standard defines the minimum experimental evidence that shall be provided in order to validate the use, in regions of high seismic risk or for structures assigned to satisfy high seismic performance or design categories, of a weak beam/strong column moment frame not satisfying the requirements of Chapter 21 of ACI 318-99.
Consistent with the ACt 318-99 requirement for analysis. ACI 374.1 specifies that, before the testing mandated by the Standard, a design procedure shall have been developed for prototype frames having the generic form for which accepLance is sought and that design procedure shall be used to proportion the test modules. Further, the Standard assumes that the prototype frames have forms that are essentially regular. having no significant physical discontinuities in plan or in vertical configuration or in their lateral-force-resisting systems. and that the frames satisfy some. but not all, of the requirements of Chapter 2). Such frames might. for example, involve use of precast elements, precast prestressed elements, post-tensioned reinforcement, or combinations of those elements and reinforcement. PrescripLive requirements for moment frames constructed with such elements are not included in ACI 318-99. Such frames might also, for example. use alternate methods, other than those specified in Chapter 21, (or force transfer through beam- column joints.
The provisions of this Standard are intended to supplement the provisions of Chapter 21 of ACt 3)8-99 and not to supplant them.
1 .0—Notation
Only symbols additional to those in AC! 318-99 are defined.
maximum lateral resistance of test module determined from test results (forces or moments)
= nominal lateral resistance of test module determined using specified geometric properties of test members, specified yield strength of reinforcement. specified compressive strength of concrete, a strain compatibility analysis for flexural moment strength. and a strength reduction factor of I .0
= probable lateral resistance of lest module determined using actual geometric and material properties of test members, an analysis for probable flexural moment strength of beams based Ofl strain compatibility and including strain-hardening effects in the reinforcement, and a strength reduction factor of I .0
column overstrength factor used for test module drift ratio
= relative energy dissipation ratio
R1.O—Notatlon
Only symbols used in this Commentary that are additional to those in Appendix E of ACI 318-99 and Standard TI. 1-01 are defined in the following:
= area of hysteresis loop
E,. E, = peak lateral resistance jar positive, negative. loadmg for third cycle of loading sequence
= fricior on live load defined in R2.6
= height of column of test module, in. or mm
= initial stiffness for positive, negative, loading for firsi cycle
,. 2 = drift ratios at peak lateral resistance for positive. negative, loading for third cycle of 10(1(1mg Sequence
0/. 0,’ = drift ratios for zero lateral load for unloading at sriffnesses K. K’ from peak positive, negative,
2.1 Drift ratio—Angular rotation under load of the column chord of the test module with respect to the beam chord. where the chords are the straight lines connecting the centroidal axes of the points of contraflexure in the beam and the column, respectively, or the centroidal axis at the point of contratlexure to the centroid of the beam-column joint in the case where a member extends on one side of the joint only.
R2. I Where a column exists on both sides of the joint, its chord is defined by the line joining the loading (or support) points. The sante is true for a beani i/wi exists on both sides of the joint. If a colwnn or bean exist on one side of the joint only, then the chord is defined by the line joining the end loading (or support) point and the joint centerline.
The drift ratio 0 concept is illustrated in Fig. R2. I for an exterior column-beam module. The position of the module at the start of testing, with its self—weight only acting, is indicated by brokemi lines. The module is pin supported at A and roller supported at D. The self weight is taken by vertical reactions VAD and VJ)1) Thai weighs, however, al.so causes a twisting about the centroid B of the joint so that opposing horizontal reactions, HAD and HCD, develop. Under self weight alone, the pin at C must he constrained to lie on the centroidal axis of the column that passes front C through B to A. That chord is the vertical reference line for drift measurements. The setup also constrains tile chord joining the centroid of the joint B and the ceniroid of the section at D to be horizontal.
For acceptance testing, a lateral force HCF is applied to the column through the pin at C and results in the specimen taking up the deformed shape indicated by solid lines. The laieral force causes reactions HAL at A and VOL ai D. The column at C displaces laterally by an amount . The chord defining the reference axis for the beam, however, remains horizontal. The drift ratio is the angular rotation of the column chord with respect to the beammi chord and for the setup shown equals ./h where Ii 5 the columnmi height and equal to the distance between the pin at A amid that at C.
2.2 Moment frame—Space frame in which members and joints resist forces through flexure, shear and axial force.
2.3 Oversrrengrh factor—Ratio of the sum of the nominal flexural strengths of the columns at their interfaces with the joint to the sum of the nominal flexural moment strengths of the beams at their interfaces with the same joint.
R2.3 The column oversirength factor A should be selected so that AE is greater than tile probable lateral resistance E. it is to be expected that the maximum lateral resistance oft/se test module should be similar to In 21.4.2.2 ofACi 3)8-99 the ratio oft/ic sum of the moments at the faces of tile joint, corresponding to the nonmuw! flexural strengths of the colwuns framing into that joint, to the suns of the main cats at i/ic faces of the joint, corresponding to tile
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