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+ti <br />I�:r. Call:.han - 5eptember 20 <br />Yage 2 <br />';��,iD11iU - <br />ixcept for a design ch�age involvin� 40-grade "���hisker" b:�rs ocr�dee � <br />�.11 weld bars on this•p-�Ject involve 60-6r.�de resteei. `_'his „ <br />rebes is difSicult to r.�-!c: and requires special :nd relatively costly <br />welding procedures (cor�p�red to �0-gr�de rebr,r). �ts use us z weld � <br />design element is unusu�:.l in my experience �nd seen.s particulerly <br />unusual in a project <:pparently desi�ned to meet only mii�imum code <br />requirements. <br />11 welds in the lo�•:er wing, in �.ibout ten p�nel closures on the west <br />end of Lii�e 7 and in the support plate assemblies on Line fi and at <br />I.ine 12-i� were welded �ai�h .:-�018 electrod�,s, without preheating of <br />the 60-grade reb�tr and without proper prehe•ating and storage uf the <br />electrodes. it is my understanding that these practices degrade the <br />welds in the following w4ys: 19elds with 7018 electrodes, if correctly <br />executed, match the strength of 40-grade, rather Lhan60-grade rebar. <br />Llectrode noisture absorption due to improper preheating and stora;;e <br />prcduces brittle welds which break easony under stress. Failure t.o <br />prehe�C the 60-grade reb�.r impe..rts a parable brittleness to the <br />steel. iL seems apparent th::i these procedures he.ve reduced Lhe <br />stren�th oi the affected welds below (.>nd perhapa �ppreci��bl,, elow) <br />the stren�th of correctly executed welds o£ 60-grade steel. <br />�iO1�CiZL2�++ � <br />lii-earl,y conerete ��r�s used con�istently by the Contractor in pours <br />the.t i inspected. ._side Prom cosmetic effects such :s s'.lrink::,;e <br />cracks due to r4pid drying and poor finishing qu<_lities, the �.ccel- <br />er�.ted set of this concrete in hot, sunny �ti�e.-tiher m�.kes i-t expedient <br />to place ii �,�ithout undue de1:.Y. �espite reminders, the Contractor <br />f�_iled to meei this recuirement un several pours �:nd a ciisproportionzte <br />mount of conc���tie �;.. a return�:d i�o the plr�nt, ._ <br />z: result. Concrete <br />cylinder break Gt:rengths appeax' high enough tro_me to u�faet:any�'snb- <br />3tandard pructices that I observed. ?n �ddii;inn to rejected concrete, <br />sir�cll pours oi 3ae 5"�-�� 5z y�-z'ds, musti h�ve involved er.,r:-ordin�.rily <br />hi;;h per yard cost for the concrete l;oured, if normc.l pumping !'h=.1'ge5 <br />�:ere involved. <br />ii;�":i��.`11:+� :.1\.l. IZliY:�.1ct�:11 li�Jl\:il:iUC'�:.U1� � <br />L�m�ge to the on-�r�de, unreinforced slr.b n:,s Leen extensive. : l�rge <br />section oi the sl;�b in the cent.ral portion ��i the lower level h<.s <br />broken up, app�rently �-s '- result oi in::degu�.'ce comp�.ction of the <br />underlying b�se. 'ihi� section .:nd sever�:l smaller sections which <br />h-:-ve :lso subsided will require repl�_cement. ..iter pouring �= large <br />portion of the lower level sl��b up to the ,�eri:.ieter strip, the <br />Contractor begc:n extensive exc �vation during ��hich the slab was <br />undercut �+long Line 1. :,s a result, large sections of the sl�•.b broke <br />ofS �nd fell into the excavGtion. ln the upper level, in�dequa.,e <br />compaction does not appear to be a problem, but cracks which appe«r <br />to me to be due ;.o lo�.ds rather th�n shrink�ge h�ve occurred. l <br />inglthe perimeter1stripeatmLined71becausentheyContractorsplansdtoin- <br />J <br />