M A S O N R Y. Winter Engineering Notes For Design With Concrete Block Masonry. Design of Anchor Bolts in Concrete Masonry

Transcription

1 M A S O N R Y Winter Engineering Notes For Design With Concrete lock Msonry C H R O N I C L E S... Introduction Anchor olts in Concrete Msonry Design of Anchor olts in Concrete Msonry This edition of Msonry Chronicles will discuss the design of nchor olts in concrete msonry nd highlight the differences in the requirements of the 006 Interntionl uilding code 1 (IC) nd the 009 IC. For msonry design, the 006 IC references the 005 edition of uilding Code Requirements for Msonry Structures 3 (ACI530-05/ASCE 5-05/ TMS 0-05) or simply ACI The 009 IC references the 008 edition of uilding Code Requirements for Msonry Structures (TMS 0-08/ACI530-08/ASCE 5-08/) or simply TMS The requirements for nchor olts in the new code hve chnged significntly in the ltest edition of the code. The primry chnges include the following: Correction of n idiosyncrsy of the 005 edition tht resulted in lrge differences in the llowle lods on nchor olts when using llowle stress design in comprison to vlues otined using strength design. Reorgniztion of the nchor olt requirements so provisions tht re pplicle to oth llowle stress design nd strength design re locted in Chpter 1. This includes the requirements for olt plcement, effective emedment lengths, nd the clcultion of projected res for tension nd sher. Addition of nchor olt filure modes tht were not included in the previous code. Tles 1 nd show comprison of the filure modes considered in the 006 IC nd 009 IC for tension nd sher, respectively. Concrete Msonry Assocition of Cliforni nd Nevd

2 Tle 1 Tensile Filure Modes for Anchor olts on Msonry 006 IC/ACI IC/TMS 0-08 Allowle Stress Strength Design Allowle Stress Strength Design Design Design Msonry Tensile rekout Yes Yes Yes Yes Steel Tensile Yield Yes Yes Yes Yes Anchor Pullout (ent-r olts Only) - Yes Yes Yes Tle Sher Filure Modes for Anchor olts on Msonry 006 IC/TMS 009 IC/TMS 0-08 Allowle Stress Strength Design Allowle Stress Strength Design Design Design Msonry Sher rekout - Yes Yes Yes Msonry Sher Crushing Yes - Yes Yes Anchor Sher Pryout - - Yes Yes Steel Sher Yielding Yes Yes Yes Yes Anchor olt Plcement Requirements Anchor olts cst in msonry re usully heded or ent-r nchor olts s shown in Figure 1. Heded olts typiclly hve hexgonl or squre hed. entr olts re usully either J or L olts. Since these re the most commonly used olts, the code provisions pply to these types of olts. Other olts, such s post-instlled nchors my e determined y testing in ccordnce with ASTM E8. 5 The MSJC code requirements specify tht the minimum effective emedment depth of nchor olts, l, e olt dimeters or inches, whichever is greter. Figure 1 illustrtes the effective emedment depth for the vrious types of nchor olts. The effective emedment depth for heded olts is equl to the length of emedment perpendiculr from the surfce of the msonry to the ering surfce of the nchor hed. For ent r nchor olts, the effective emedment depth is mesured s the distnce perpendiculr from the surfce of the msonry to the ering surfce of the ent end minus one olt dimeter. As shown in Figure 1, there must e grout spce of t lest 1/-inch of grout etween olts nd the msonry unit. Note tht the code permits the grout etween the olt nd the msonry unit to e reduced to 1/-inch if fine grout is used. The cler distnce etween prllel nchor olts must not e less thn the dimeter of the olt or 1 inch. Strength Design of Anchor olts Figure 1 Anchor olts in Concrete Msonry Anchor olts must e emedded in grout. The code permits 1/-inch dimeter olts to e plced in mortr eds tht re t lest 1/-inch thick. However, this is not commonly done. There ws some confusion in the previous code, with some interprettions requiring tht ll msonry with nchor olts must e grouted solid. This hs een clrified in the new code. olts my e plced in prtilly grouted wlls, s long s the effect of open cells or hed joints is considered. Tensile Strength of Anchor olts In TMS 0-08, the tension filure modes considered nd the equtions for clculting the strength corresponding to ech filure mode re identicl to those in the 005 code. However, the nomenclture hs een slightly modified to e more consistent with other prts of the code. As illustrted in Tle 1, three filure modes re considered when determining the tensile strength of nchor olts. Since nchor pullout is only considered in ent-r olts, only two filure modes re considered for heded olts.

3 The nominl xil strength of n nchor olt, n, is the smllest of the vlues otined from the following equtions for the vrious filure modes: Msonry tensile rekout (φ = 0.5): = A f ' (1) n pt m Steel tensile yield (φ = 0.9): ns = Af () Anchor pullout (ent-r olts only, φ = 0.65): ( ) np = 1.5 f' m ed + 300π l + e + d d (3) where d nd A re the olt dimeter nd crosssectionl re, f m is the compressive strength of the msonry, f y is the yield stress of the nchor olt nd e is the projected leg extension of ent-r nchor, s shown in Figure 1. The term A pt represents the projected tension re of right circulr cone on the msonry surfce. As shown in Figure, the projected tension re is given y: A pt = π l () where l is the effective emedment length of the olt. The projected re should e reduced y ny portion tht lies outside the msonry or overlps n open cell or open hed joint. In ddition, when the projected res of djcent olts overlp, the vlue of A pt should e djusted so tht no re is included more thn once. Figure 3 shows some exmples djustments to the of the projected tension re. Figure 3 Exmples of Adjustments to Projected Tension Are Sher Strength of Anchor olts The provisions for determining the sher strength of nchor olts using strength design hve een modified in the new code. As shown in Tle, msonry sher crushing nd nchor sher pryout hve een dded to the msonry sher rekout nd steel sher yielding filure modes tht were considered in the previous code. The nominl sher strength of n nchor olt, v, is the smllest of the vlues otined from the following equtions: Figure Tension Filure y Msonry rekout Msonry sher rekout (φ = 0.5): = A f ' (5) vn pv m

4 Msonry sher crushing (φ = 0.5): Msonry tensile rekout: = f A (6) 1050 vnc ' m Anchor sher pryout (φ = 0.5): = 1.5 A f ' pt m Steel tensile yield: (11) =.0 = 8 A f ' (7) vpry n pt m s = Af (1) Steel sher yielding (φ = 0.9): Anchor pullout (ent r elts out): vns = 0.6Af (8) ( ) p = 0.6 f' m ed + 10π l + e + d d (13) The projected sher re of hlf of right circulr cone, A pv, is used to clculte the strength in the sher rekout filure mode. A pv π le = (9) where l e is the distnce to the edge of the msonry mesured in the direction of the pplied sher lod. As with the tension pullout cone, A pv must e reduced to ccount for overlpping res of closely spced olts or for portions of the re tht lie outside the msonry. Comined Axil Tension nd Sher Tests on nchor olts indicte tht liner interction reltionship provides conservtive estimte of the llowle lods on olts sujected to oth sher nd tension. Thus, llowle lods re determined with the following eqution: The terms in the ove equtions, including the projected tension re, re the sme s those for strength design, including the projected tension re. This is different from the previous code, which required tht the projected tension re e clculted using the edge distnce l e, when the edge distnce ws less thn the effective emedment depth. Allowle Sher Lod of Anchor olts As with the llowle tensile lods, the equtions for clculting the llowle sher lods on n nchor olt, v, re modifictions of the strength design equtions: Msonry sher rekout: = 1.5 A f ' v pv m Msonry sher crushing: (1) f φ n + vf 1 φ (10) vn where f nd vf re the fctored tension nd sher lods, respectively. Allowle Stress Design of Anchor olts Allowle Tensile Lod of Anchor olts f A 350 vc = ' m Anchor sher pryout: =.0 =.5 A f ' vpry pv m Steel sher yielding: vs = 0.36Af (15) (16) (17) TMS 0-08 considers the sme tension filure modes for llowle stress design s strength design, with the equtions modified to working vlues. This is different from the previous code, which did not consider nchor pullout for ent-r olts nd used equtions tht typiclly resulted in significntly lower vlues when compred to strength design. The llowle xil tensile lod of n nchor olt,, is the smllest of the vlues otined from the following equtions for the vrious filure modes: Comined Axil Tension nd Sher Similr to strength design, liner interction digrm is lso used for llowle stress design when there is comintion of tension nd sher lods on n nchor olt: v + 1 v (18) where nd v re the unfctored tension nd sher lods, respectively.

5 Exmple Determine if the 3/-inch dimeter nchor olts shown in Figure cn resist the comined tension nd sher lods on the wll connected to flexile diphrgm. Two olts with yield stress of 36 ksi, n effective emedment length of 6 inches re spced 7 inches prt every feet, s shown in Figure. The projected extension of the ent r is inches. The msonry compressive strength is 1500 psi nd the weight of the wll is 78 psf. The short period spectrl ccelertion, S DS =1.g. Therefore, the tension on the connection is given y: F = 0.96(1053) = 1011 ls/ft p The sher on the connection is equl to: ( S ) P = ( )80 = 115 ls/ft DS D The nominl tensile strength of ech olt is clculted using the smller of Equtions (1), () nd (3). Without correction, the projected tension re for ech olt would e: A pt = πl = π(6) = 113 in However, since the spcing etween the two olts, s, is less thn two times the effective emedment depth, l, there is overlp of the projected tension re of djcent olts. From Figure 3, the djusted tension re is given y: 1 Apt ' = πl l θ θ ( sin ) where θ is in rdins nd is given y: 1 s l θ = cos For the exmple: 1 s 1 7 θ = cos = cos 1.9 rdins l = 6 Figure Anchor olt Design Exmple Strength Design Solution Consider the lod comintion 1.D+1.0E, which governs y inspection. From ASCE 7-05, the out-ofplne nchorge force for wll connected to flexile diphrgm is given y: F = 0.8S IW p DS p where I is the importnce fctor nd W p is the wll weight triutry to the connection. Assuming tht I =1.0: F = 0.8S IW = 0.8(1.)(1.0) W = 0.96W p DS p p p The triutry wll weight is equl to: W p 0 = = 1053 ls/ft And the modified projected tension re is equl to: 1 Apt ' = πl l θ θ ( sin ) 1 = 113 ( 6) ( 1.9 sin1.9) = 96 in The tension cpcity of ech olt due to msonry rekout is thus given y Eqution (1): φ = φ A ' f ' n pt m = 0.5()(96) 1500 = 736 ls From Eqution (), the olt tension cpcity due to yielding of ech nchor olt is equl to: φ ns = φaf = 0.9(0.)36000 = 1,56 ls

6 nd the olt tension cpcity due to nchor pullout is given y Eqution (3): { 1.5 ' 300 ( ) } φ = φ f ed + π l + e + d d np m 1.5(1500)()(0.75) = π ( ) 0.75 = 937 ls For the cpcity of the olts in sher, the msonry sher rekout filure mode cn e ignored since the distnce to the edge of the msonry in the direction of the lod is lrge. For msonry sher crushing: φ = φ f A 1050 vnc ' m The llowle tension on ech olt is given y the smllest of: = 1.5 A f ' pt m s = 1.5(96) 1500 = 68 ls = 0.6Af = 0.6(0.)36000 = 950 ls ( ) ( ) = 0.6 f' ed + 10π l + e + d d p m = 0.6(1500)()(0.75) + 10π = = Anchor sher pryout: (0.5)1050 (1500)(0.) 661 ls vpry = φ8 Apt f ' m = 0.5(8)(96) 1500 = 187 ls Steel sher yielding: φ vns = φ0.6af = 0.9(0.6)(0.)(36000) = 855 ls Since ech group of two olts is spced t 8 inches on center, the interction eqution is given y: f φ n vf + φ vn 1011() 115() = + = OK (736) (661) = 5739 ls Ignoring the msonry sher rekout filure mode, the llowle sher on ech olt is the smllest of: f A 350 vc = ' m = = 350 (1500)(0.) 177 ls =.5 A f ' vpry pt m vs =.5(96) 1500 = 995 ls = 0.36Af = 0.36(0.)(36000) = 570 ls Using the smllest of the vlues in tension nd sher, the interction eqution is given y: Allowle Stress Design Solution v + v Using the lternte sic lod comintion in the IC, the governing lod comintion is D+E/1.. The tensile lod on the connection is: = + = OK (68) (177) 1011() = = 889 ls/ft 1. The sher on the connection is equl to: = 80() = 30 ls/ft v

7 Conclusions The new code provisions for designing nchor olts hve een updted to include more filure modes nd to ensure consistency in designs using different methods (strength design nd llowle stress design). Prior editions of the code resulted in llowle stress designs for nchor olts tht were often extremely conservtive when compred to those otined using strength design. The new codes, on the other hnd, result in similr designs. References 1. ICC, 006 Interntionl uilding Code, Interntionl Code Council, Inc., Country Clu Hills, Illinois, ICC, 009 Interntionl uilding Code, Interntionl Code Council, Inc., Country Clu Hills, Illinois, MSJC, uilding Code Requirements for Msonry Structures (ACI /ASCE 5-05/TMS 0-05), Reported y the Msonry Stndrds Joints Committee (MSJC), Americn Concrete Institute, Frmington Hills, Michign, 005. Aout the Author Dr. Chukwum Ekwueme is n Associte Principl with Weidlinger Assocites, Inc. He received his Eng from the University of Nigeri nd MS, DEng, (Degree of Engineer) nd PhD Degrees from the University of Cliforni, Los Angeles. He is registered Civil nd Structurl Engineer in the Stte of Cliforni. Dr. Ekwueme is memer of the Msonry Stndrds Joint Committee (MSJC) nd on the ord of Directors of the Msonry Society (TMS). He is lso ctive in severl other orgniztions such s the Americn Society of Civil Engineers (ASCE), Structurl Engineers Assocition of Cliforni (SEAOC) nd the Americn Concrete Institute (ACI). Dr. Ekwueme hs written severl pulictions nd co-uthored CMACN s Seismic Design of Msonry Using the 1997 UC, nd the 006 edition of Design of Reinforced Msonry Structures. He hs lso received wrds for his work s structurl engineer.. MSJC, uilding Code Requirements for Msonry Structures (TMS 0-08/ACI /ASCE 5-08/), Reported y the Msonry Stndrds Joints Committee (MSJC), The Msonry Society, oulder, Colordo, ASTM, Stndrd Test Methods for Strength of Anchors in Concrete nd Msonry Elements, Stndrd ASTM E88-96 (003), Volume 0.11, ASTM Interntionl, West Conshohocken, Pennsylvni, 009.

8 Concrete Msonry Assocition of Cliforni nd Nevd 6060 Sunrise Vist Drive, Suite 1990 Citrus Heights, CA (916) Presort Stndrd U.S. Postge PAID Premit No. 60 Scrmento, CA CHANGE SERVICE REQUESTED Concrete Msonry is Sfe & Sound. Contct CMACN with Requests for Design Seminrs t (916) or info@cmcn.org Now Aville: 006 Design of Reinforced Msonry Structures, CMD06 Computer Progrm, Typicl Msonry Detils CD includes AutoCAD nd PDF formts Concrete Msonry Assocition of Cliforni nd Nevd (CMACN) is plesed to introduce updted products for prcticing engineers. Orders cn e plced on line t (ll crds ccepted) or y clling (916) (Vis nd MsterCrd only). CMACN PRODUCER MEMERS Producer Memers re n individul, prtnership, or corportion, which is ctively engged in the mnufcture nd sle of concrete msonry units. Air Vol lock, Inc. Angelus lock Compny, Inc. slite Concrete Products, LLC locklite ( susidiry of slite Concrete Products LLC) Clstone Compny, Inc. Cstlelite lock LLC CEMEX Cind-R-Lite lock Compny, Inc. Desert lock Compny, Inc. Oldcstle APG West, Inc. ORCO lock Compny, Inc. RCP lock & rick, Inc. Tri Delt ( division of Oldcstle APG West, Inc.)