Empire State Building Structure Magazine-Books Pdf

Empire State Building STRUCTURE magazine
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Like other buildings of its era the Empire State Building walls work. because they are thick solid composite masonry Gravity loads are re. lieved at each floor into the building structure so gravity load stress does. not accumulate in the masonry It can be rationalized and empirically. confirmed that the thermal expansion and contraction of the masonry. is minimized because the heat sink,effect of the massive masonry and Figure 6. embedded steel Stress resulting,from the initial expansion of the. brick masonry also unloaded one,floor at a time into the floor span. drel beams,Wind movement is minimized,by the very stiff structural steel. t frame which weighs in at a hefty 60 pounds per square foot of floor. p y area with columns spaced at approximately 20 feet on center compared. Drawing courtesy of Architectural Forum Magazine June. to about half that weight per square foot and 30 to 45 foot column. causing corrosion of the iron strap anchors attaching the limestone to. spacing in modern high rise buildings Movement of the structural steel. the brick back up wall At these locations as the iron anchors corroded frame of the Empire state Building is thus relatively low in comparison. the corrosion product expanded causing a shard of the limestone to pop to modern high rise buildings with optimized therefore lighter and. out and severely diminishing the limestone anchorage capacity The more flexible structural steel frames. parapet walls were severely deteriorated as a result of water infiltration. which caused corrosion of the steel spandrel beams and also freeze. Fa ade Repair Program,thaw damage to the masonry At.
the building corners the stone In 1989 a program of fa ade repair was specified by the Thornton. was cracked and many years ago, Tomasetti Group and work was begun by A Best Contracting This. steel straps had been bolted on to work included cutting all of the existing limestone joints to a depth. the surface of the limestone in an, of about inch Closed cell polyethylene foam backer rod and Sika. attempt to confine the limestone, polyurethane sealant were then installed in the limestone masonry. cladding in place Figure 6 joints The unorthodox installation of sealant at the front of the. Figure 4 Like many solid masonry clad limestone joints provides further protection against the infiltration of. buildings of this time period water through the many joints between the limestone panels Although. there were no surface visible soft joints in the fa ade masonry to these sealed joints also prohibit expiration of moisture out of the. handle the initial column shortening temperature and moisture masonry and this practice is therefore usually not desirable moisture. expansion and wind movement Archival research and later invasive evaporation from the wall is more than adequately provided for by. investigation did identify that a compressible filler consisting of the large area of vapor permeable limestone The joints between the. corrugated lead lined top and bottom with sheet lead was installed limestone units will be kept weather tight by the low elastic modulus. in the bed joint at the eight inch thick key stone It appears that this polyurethane sealant. compressible layer did serve very well to accommodate permanent The wall surface was sounded to detect latent spalls at the corroded. shortening of the steel structure during erection because as we later iron anchors A new anchor was installed to replace the function of. found these lead strips were compressed solid in the stone joints each corroded iron anchor that was removed Some of the new anchors. At some point these joints had apparently been re cut and pointed were Dur o wall stainless steel threaded rods with mechanical brass. and thus apparently they provide minimal ability to accommodate expanders at each end that engaged the brick back up masonry and. additional strain Yet in our investigations of the masonry facade no the limestone In other locations epoxy adhesive was used to anchor. significant damage related to compressive stress was evident threaded stainless steel rods for the same purpose The shards in the. limestone and the corroded iron anchors were saw cut and removed The. Figure 5 exposed stone was grooved and 3 inch diameter stainless steel wire. anchors were embedded in the limestone Figure 8 The voids in the. limestone were filled with specially formulated Jahn repair mortar that. matched the thermal expansion and moisture absorption rate of the. surrounding limestone At parapet locations where the spandrel beams. had been severely damaged by corrosion the displaced limestone and. brick back up masonry was removed the structural steel was repaired. and epoxy coated and the masonry was replaced At cracks in the. large limestone units at the building corners the initial plan was to. use epoxy set stainless steel pins to stitch the stones together and to the. brick masonry back up wall and this work commenced. In 1989 an investigation of the 6400 window frames and adjacent. interior walls was performed The original anchorages of the existing. windows to the brick masonry were found to be in good condition. However the steel window frames and the double hung sash frames were. severely corroded and the weather stripping was in poor condition. STRUCTURE magazine 40 January 2006, It is interesting to note the sight lines maximized The sash is glazed with insulated glass units. that the Chrysler Building The new frames are thermally broken accomplished by connecting. featured in the December the front and back extrusions with a continuous cast in place section. 2005 issue of STRUCTURE of polyurethane which has a much lower thermal conductance rate. magazine which was built than aluminum The condition of the steel sub frame and anchors into. at approximately the same the brick masonry were in good condition and so they were re used. time has similar steel framed The new windows were screwed to the Campbell steel sub frames. windows However these with self drilling tapping stainless steel screws The joints at the outside. were originally galvanized perimeter of the windows were sealed with Sika polyurethane sealant. while the windows at the to the stainless steel mullions at the jambs and to the cast aluminum. Empire State Building were spandrel panels at the sills and heads. originally painted After 60 There are 19 separate roof areas on the building totaling 33 380. years of service the Chrysler square feet in area The roofs were originally built up multiple ply coal. Building s windows were in tar roofs with quarry tile walking surfaces in mortar setting beds Over. much better condition than t the years most of the roofs had been covered with additional layers. those in the Empire State y of built up roofing with stone ballast above that By 1989 many. Building Repair of the origi Co p of the roofs were leaking both into the interior spaces and into the. nal windows was studied but fa ade walls A roof replacement program was executed The roofs were. it was found to be impracti stripped down to the concrete slabs New counterflashing pockets. cal The 12 existing coats of Figure 7 were created at the inside face the parapet walls Polyisocyanurate. paint over the corroded steel foam insulation board was installed and covered with an adhered. would have had to be removed and the steel prepared and treated with single ply EPDM membrane The membrane was then covered with. two or three coats of new paint This would have involved removal of a protection board and concrete pavers in a terra cotta color similar. the sash for surface preparation and painting requiring temporary clo to the original quarry tiles The replacement roof for the high traffic. sure interior restoration and tenant disruption Work on the steel win observation deck was specified and executed by others using Kemper. dow frames in place would have been tedious and costly especially with liquid applied polyester roof membrane also topped with protection. lead paint removal safety issues Corrosion of inaccessible surfaces of. the frame and sash would undoubtedly have continued with no guar. board and concrete pavers,continued next page, antee of the durability of the repaired windows even after spending.
millions of dollars for repair work Since the original sash did not tilt Figure 9. or rotate window washing had to be done from the outside typically. by personnel tied back to buttons on the window frames This meth. od is currently not acceptable by OSHA and certainly the corrosion of. the frames made this procedure even less safe than in the past. Replacement windows were specified as Series 9000 windows. manufactured by TRACO These replacement windows have several. important features The windows were designed to pan over the. existing Campbell steel windows The existing window paint coat. ings were tested to determine the original color of the windows The. original red color was matched on the replacement windows The new. double hung tilt windows have aluminum frames and sash with very. narrow profiles to keep the total width of the metal minimized and. STRUCTURE magazine 41 January 2006, The next step of the corner rebuilding work was the removal of. the limestone and brick masonry back up wall at the corners A Best. Contracting had made extensive use of suspended scaffolds for most. of the general fa ade repair work Most of this work involved cutting. sealant anchor pins and mortar installation and the relatively light. duty suspended scaffolds were well suited to this work However. for the masonry replacement and steel modifications at the building. corners they used a relatively new approach for executing the work. Steel support dunnage was installed at the 25th and 30th floor roof. setbacks and a trussed tower was installed on one side of each of the. eight corners up to the 72nd floor setback roof at three corners at a time. The trussed towers were laterally anchored to the building with epoxy. adhered threaded studs through the fa ade masonry into the concrete. behind the building s outer steel spandrel beams The scaffold tower. t was a variation of the more typical rack and pinion construction. y hoist but instead of a cab it had two independently operating L. Co p shaped platforms on each tower that wrapped the corner work area. with a 7 000 pound capacity enclosed work platform This equipment. facilitated installation of the limestone units which weighed up to. 1 500 pounds each and access by labor to the work areas. The first step of the corner rebuilding work was the removal of the. limestone and brick masonry back up wall at the corners Fortunately. i n investigation had shown that the corrosion damage to the structural. steel was limited to the outboard surface of the columns and spandrel. beam ends with diminishing deterioration at about six inches back. into the brick masonry steel interface, g a At the corners with limestone masonry cracks the severely corroded. structural steel columns were stripped of masonry and all exposed steel. was power tool cleaned to meet the requirements of SSPC SP11. Major Repair Of The Corners which requires removal of all loose corrosion products to a sound bare. During the course of the repair of the field of the fa ade roofs and surface Two coats of epoxy paint were then applied to the steel to. windows it had become very clear that the cracks at the corners of the protect the steel from corrosion Care was taken to avoid removing. building were indicative of a problem that could not be fully addressed the full thickness of the brick masonry abutting the steel columns so. by surficial repairs of the limestone masonry that the occupied tenant space remained enclosed at all times Figure. The mostly vertical cracks in the limestone facing and brick 10 Custom fabricated stainless steel Z clips were connected to the. masonry back up at the building corners were probed to confirm that columns with Nelson threaded stainless steel studs to positively. the cracks were directly correlated to conditions of outward expansion engage the now discontinuous fa ade wall after demolition of the cor. resulting from corrosion of the structural steel Figure 7 However ner masonry It was efficient to do all of the demolition in one phase. the amount of section loss at the structural steel framing sections so it was necessary to leave the corners excavated for a few months time. was for the most part structurally insignificant A detailed survey and over the winter Installing temporary tarps would have caused more. invasive probes provided correlation between the degree of limestone damage to the limestone at anchorage points and would have been. cracking at the eight corners of the tower and the severity of corrosion difficult to maintain in this very windy exposure It was decided that all. of the structural steel building columns within the corner piers. Several alternatives for restoration of the fa ade at the building corners Figure 11. were studied including replacement in kind replacement with pre cast. concrete and replacement with glass fiber reinforced concrete panels. After a process of value engineering the final scheme included localized. replacement in kind The repair scheme was influenced by the extent of. the repairs the logistics of working up to 85 stories high on the exterior. of an occupied building in mid Manhattan the need to improve on the. original anchorage and support of the stone to repair and to protect. the vulnerable structural steel and of course to preserve the original. appearance and integrity of this historic landmark building. A significant cost saving was realized by not replacing the entire corner. piers Once it was confirmed that only the masonry directly in front. of the columns was damaged it became feasible to replace only that. masonry Because of this approximately three feet of masonry pier. width at each side of the corner had to be removed and approximately. three feet between the window jamb and the removal line could be. pinned in place and restored The remaining limestone panels were. re anchored to the brick back up masonry with 2 inch diameter. threaded stainless steel rods set in epoxy Figures 5 and 9. STRUCTURE magazine 42 January 2006, tracks with the horizontal bed joints in the limestone facing to. follow When the replacement limestone was installed custom made. 3 inch thick stainless steel split tail anchors with vertical slots to. allow adjustment were bolted to the Unistrut tracks and the split tail. anchors were engaged into slots cut into the edges of the new limestone. units Figure 13 The new stainless steel anchors will not cause the. same type of corrosion failure that deteriorated the original plain iron. strap anchors and caused cracking and spalling of the original stone. The foam was later removed and the voids above and below the tracks. were filled solid with mortar, The limestone used for replacement at the corners was quarried from. the same quarry as the original stone in Bedford Indiana Construction. Figure 12 of a full size mock up of a story high corner section and a rack of multi. ple full size stones were constructed at the quarry A range of colors and. t and textures was agreed upon and the accepted stones were then cut in half. righsurface, voids and spaces between the bricks and between the masonry.
y One half was used at the, the steel would be filled with mortar and that the demolition. fabrication shop for stone, would be coated with a vapor permeable Portland cement sand and. and finish quality control, acrylic product manufactured by Sonneborn called Sonoblok This. and the other half stones, coating successfully sealed the disrupted masonry until the steel and. were used at the building,the masonry was replaced months later.
for appearance verifica, The limestone support configuration in the corner masonry. tion The limestone ma, replacement area was modified by welding on structural steel supports. terial was also subjected, directly under the eight inch thick stone course Figure 11 The. to extensive laboratory, limestone at the rebuilt corners is now directly supported by the. tests for compressive and, structural steel rather than by the brick masonry as in the original.
tensile strength and for, construction It is interesting to note that like many of the buildings. water absorption Fabri, of this vintage there is no flashing over the structural steel beams. cated stones including, nor is there any weep system to allow drainage of water out of the. many L shaped corner, wall assembly Rather than change this concept in a localized zone. stones were shipped by, it was decided that the two coats of Tnemec epoxy coating would.
truck to New York City, adequately protect the prepared structural steel surfaces and that. The stones were brought, the concept of filling every void in the wall with mortar would be. down to the building cel, maintained in the replaced masonry making drainage and flashing. lar and inspected again, less important than it would be in a cavity wall system. The stones were then,transported upstairs by,Figure 13 freight elevator to a con.
venient location and pass, ed out through a window opening onto the work platform which car. ried them within inches of their installation location. After the brick masonry cured for about a week the limestone. was installed All of the collar joints which are the vertical spaces. between the masonry wythes were filled solid with mortar The. mortar was sampled and compression tested at seven and 28 days. All limestone head and bed joints were filled with ASTM type N. mortar to within inch of the front face Closed cell polyethylene. foam backer rod and urethane sealant were then installed at the. front of the limestone masonry joints Figure 14, A lesson that was reinforced on this project is that when engineers. work on vintage buildings it is challenging to understand the intent. of the original designers and to be sensitive about how modern de. In the replacement phase thousands of two inch long 3 inch sign and detailing practices are combined with very different older. diameter stainless steel threaded Nelson anchor studs were welded to design practices. the columns and triangular wire masonry ties were then connected The Empire State Building fa ade is now ready to face the next 60. to the threaded studs Half inch diameter threaded stainless steel years of its service with of course regular maintenance. Nelson studs were welded to the steel columns to anchor stainless. steel Unistrut tracks placed horizontally in alignment with the. horizontal joints in the limestone to be installed later Figure 12. The severe weathering rated bricks were set in ASTM Type N mortar Robert J Nacheman P E is a Principal Thornton Tomasetti. to fully encase the structural steel and to bring the brick back up Group Inc LZA Technology Division in Newark New Jersey Mr. masonry to within one inch of the back of the new limestone panels Nacheman can be reached at RNacheman TheTTGroup com. Temporary foam inserts were placed above and below the Unistrut. tracks to allow for additional vertical adjustment to align the Unistrut.

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