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. 29.84/3-7:2 PRESERVATION eservatiooTech Notes,... Tech Notes U.S. Departmentofthe Interior ".'S*'} NationalPark Service CulturalResources fiT 1 PreservationAssistanceDivision »UBUC DU MEWJ ' iT#*U. Ilii-ULB H >•;V~'T-).-, '7fV in APR 9 1992 MASONRY mi CLLMSOfl NUMBER in 2 III Hill Stabilization and Repair of a iiiii lllll urn Historic Terra Cotta Cornice iiiii mi' Jeffrey S. Levine »I5| John Milner Associates Hi" Hi" Donna Ann Harris Philadelphia Historic Preservation Corporation iii« f Of! ill 1 * II *M rW LAND TITLE BUILDING Philadelphia, Pennsylvania The Land Title Building is a prominent easement to the Philadelphia Historic turn of the twentieth century office Preservation Corporation (PHPC) in building, located in the heart of down- 1981. town Philadelphia. Designed by the Chi- The twenty-three story 1902 tower is cago architect, Daniel Burnham in a steel framed structure, faced with gray 1897, a second tower was added to the Connecticut granite and organized in a site in 1902 by Burnham and local ar- classical tripartite composition typical of chitect Horace Trumbauer. The two in- early skyscrapers. The tower's "capi- terconnected towers are listed on the tal" includes an enriched terra cotta Terra cotta roofcornices should be National Register of Historic Places. cornice. The cornice is approximately repaired rather than replaced The property owner conveyed a facade 465' long, projects nearly 7' from the whereverpossible. granite face of the building, and measures over 9' in height (seefigure 1). The cornice is constructed of over 1,200 terra cotta face units and has a roof comprised of a concrete and terra cotta deck sheathed with heavy gauge EXISTING BRICK PARAPETWALL EXISTING STEEL INVERTED "T" copper (seefigure 2). Two concentric rings of structural steel channels which are tied to steel girt outlookers provide ERXOIOSFTING MAIN EXISTING LEAD COATED the main support for the cornice. The COPPERAND BUILT-UP- outlookers, in turn, are cantilevered ROOFING MEMBRANES from the structural steel columns of the EXISTING LAG BOLT building. The interior of the cornice is HOLD-DOWN filled with lightweight masonry mate- EXISTING SCUPPER I jf- rials and lacks any ventilation. The backup materials consist of hollow terra EXISTING DRAIN LINE cotta blocks and brick, supported from below by wood blocking and infilled with a cementitious mix containing coke and iron slag. The roof is surmounted by a brick parapet wall, the outside face EXISTING STEELCHANNELS of which is clad with terra cotta of simi- EXISTING LIGHTWEIGHT lar appearance to that of the cornice. MASONRY BACKUP AND FILL Problem EXISTING HOLLOW Due to recent terra cotta failures and TERRACOTTA BLOCK evidence of earlier problems (seefigures 3 and 4), the architectural firm of John BRICKSOLDIERCOURSE Milner Associates was hired by the EXISTING MASONRY building owners to inspect the terra BACKUP cotta cornice of the 1902 tower. The purpose of the inspection was to deter- mine whether the cornice could be suc- EXISTINGTERRACOTTA cessfully repaired and retained. The al- (TYPICAL) ternative would be to replace the cornice in a manner consistent with the historic EXISTING GRANITE preservation requirement of the facade EXTERIOR WALL easement placed on the building. The cornice was examined utilizing Figure 1. Section through the cornice and the parapet showingthe structure's construction and aerial scaffolding that was cantilevered attachment to the building. The inverted T's areembedded in concrete and act in friction to help support thecyma recta unit from rotating outward. The testopenings did not penetrate below the off the main roof and from upper story soffit level ofthe cornice. Drawing by Jeffrey S. Levine. windows. Inspections were made in areas assumed to be most severely dete- riorated to establish worst-case condi- -136'-0" tions. Due to the extreme depth and height of the cornice and the type of scaffolding used, inspection of the entire length of the cornice was not feasible. MAIN ROOF CORNICE BRACKET- Visual inspection of the terra cotta re- BELOW (TYP.) vealed four common types of deterioration: spalls, glaze crazing, cracking, and open mortarjoints. In addition, sound- ELEVATOR ing the terra cotta units with a wooden PENTHOUSE mallet indicated that roughly 10% of the terra cotta units had cracked internal webs. Deterioration resulting in loss of PARAPETWALL CORNICE ROOF- material appeared with less frequency CORNER and was found principally at the outer PENTHOUSE scroll of the brackets (seefigure 3) and (TYP.) 1 NORTH at the scalloped fascia (seefigure 4). f % Water infiltration through holes in the TESTOPENING-3 TESTOPENING TESTOPENING cornice's roof membrane was deter- NO. 1 NO. 2 NO. 3 mined to be the primary reason for much of the terra cotta deterioration. Figure2. Roofplan ofthe 1902 tower showing the location oftest openings in the cornice roof. Each bracket was later numbered consecutively so that easy reference could be made to a particular area Water penetration had caused various ofthecornice. Drawing by Jeffrey S. Levine. steel anchors to corrode, resulting in oxide jacking. [The corrosion product of tributed to the moisture infiltration and scaling of the steel frame members ap- the oxidation of steel takes up more vol- oxide jacking problems. peared to be limited, except at the in- ume than the steel itself. Oxide jacking Test openings made in the cornice verted "T" members where conditions refers to this expansion and the conse- roof revealed much about the construc- were worse, but still not bad enough to quent displacement, cracking, and tion of the cornice and the condition and warrant replacement. spalling caused to adjacent masonry ma- integrity of the structural steel members Although based on a limited inspec- terials.] Open mortarjoints and inappro- which supported the terra cotta facing tion, the structural steel framework ap- priate past repairs, including the exten- units. Light rust was seen on all steel peared to be adequate for the continued sive use of sealants which tended to trap members, including channels, outlook- support of the cornice. Problems with moisture within the cornice, also con- ers, J-hooks, and dogs. Flaking and the terra cotta cladding of the cornice stemmed not so much from the quality of its materials and method of construction, which are good, but from inap- propriate and irregular maintenance practices over its long history. The continued integrity ofthe cornice, however, depended upon limiting further oxidation of the steel structure and anchoring devices by removing all sources of water entry into the cornice. Solution Since the underlying steel structure of the cornice appeared to be sound, the building owners, project architect, and PHPC agreed that the cornice should be retained and that a stabilization and repair program be undertaken to address the terra cotta deterioration and allay concerns over public safety. Numerous options were explored by the architect for stabilizing terra cotta units with cracked internal webs and those units considered to be highly susceptible to oxide-jacking related failure in the future. The extremely porous nature and high moisture content of the light-weight concrete fill of the cornice made the use of an epoxy anchor system impractical. Pull-out tests of mechanical expansion anchors set in the lightweight fill revealed that the holding power of the fill was negligible at about 60 psi. Mechanical anchors were found Figure3. Numerous brackets were found to be missing their outer scrolls due to oxidejackingofthe Figure4. Extreme loss ofmaterial was noted in steel J-hooks, steel pencil rods, and temporary support wires located within the units that were used thescalloped fascia above the brackets at the forinstallation. Cracking in the brackets whose outer scrolls had not yet broken offindicated southend oftheeast elevation ofthe cornice. potential for further lossofmaterial ifstabilization measures were not undertaken. Thisdeterioration and corresponding cracking During theoriginal construction ofthe cornice, the brackets were hoisted into place and in otherfascia units wasdue to rusting ofthe temporarily supported by the wires cast into the nose ofthe bracket units. J-hooks were then structural steel angle iron which supports the dropped down from the outermost steel channel above into the upper and outermost cellsformed by fascia units attheir center webs (see figure 1). theunit's internal webbing. A steel rod was then inserted horizontally through holes cast intothe A likely point ofwater entry was a large open exterior sides and internal websofthe unit such that, with minor adjustment in the length ofthe jointlocated immediately above the fascia, at J-hooks, the rod sat in the trough ofthe J-hooks; the weight ofthe bracket were thereby transferred thebedjoint ofthe cyma recta units. Photo by totheJ-hooks (see also figures 1 and 5). Photo byJeffrey S. Levine. Jeffrey S. Levine. - NEWSTAINLESS STEEL BEARING PLATEAND NUTASSEMBLY COUNTERSUNK BELOW SURFACEOFROOF DECK. FILL REMAINING CAVITYWITH GROUT. EXISTING CONCRETE DECK OFCORNICE ROOF NEW7/i6" THREADED STAINLESSSTEEL ROD INSERTEDTHROUGH 1" (MAX.) DRILLED SHAFTAND MECHANICALLY ANCHOREDATEACH END. EXISTING LIGHT-WEIGHT MASONRYFILL EXISTING STEELCHANNEL- EXISTING HOLLOWTERRA EXISTING STEELJ-HOOK COTTABLOCK EXISTING BRICK- EXISTINGWOOD BLOCKING EXISTINGVOID- EXISTING BRICK- SOLDIER COURSE NEW7/,6" STAINLESS STEEL MECHANICALANCHOR SET IN 1" DRILLED SHAFT. INSTALLANCHOR EXISTING MASONRYBACKUP WITH UPWARDANGLE. EXPANSION ASSEMBLYAT UPPER END OFANCHOR TO BE SET INTOPWEBOF BRACKETOR BOTTOM WEB OF SOFFIT UNIT NUT, WASHER, AND NEOPRENE GASKET EXISTINGTERRACOTTA AT LOWER END OFNEWANCHOR ARE SET IN COUNTERSINK. FILLCOUNTERSINKWITH EPOXY AFER SETTING ANCHOR. TYPICALCRACK PATTERN NEW STAINLESS STEELBEVELED WASHER, NUT, AND BEARING PLATE ASSEMBLYSURFACE MOUNTED ON BRACKET Figure5. Detail section through the cornice showing the manner in which the vertical and angled outer scroll anchors were installed in the bracket units. The vertical hash-marks represent a typical crack pattern found in brackets which had not yet lost their outer scrolls. All 128 brackets received angled outerscroll anchors and about 80 received vertical anchors. Drawing by Jeffrey S. Levine. to be suitable when set in brick backup Work Description the cornice. Four general categories of or in structural steel. Pull-out values of anchors were employed: vertical bracket The project work had two different from 500 to 1,800 psi were obtained in anchors; angled outer scroll anchors; these materials, without any slippage or components. The first part was to pre- fascia clip-angles; and other miscella- vent water from entering the cornice as failure. These values were sufficiently neous mechanical anchors (seefigures high to provide a working safety factor much as possible. This involved instal- 5-7). Over 750 new stainless steel an- of four times the weight of the terra lation of a new roof and drainage sys- chors, ranging in length from 9" to 6', tem on the cornice; repointing deterio- cotta unit being supported. After making were installed to secure approximately the decision to use mechanical anchors, rated mortarjoints; injecting cracks in 350 loose and cracked terra cotta units drilling tests were conducted to deter- the terra cotta with epoxy; coating spalls to the structural steel or masonry backup and areas suffering from severe glaze mine anchor depths and backup mate- of the cornice. crazing with a polyester polyurethane rials at typical anchor locations on the enamel paint; and installing patches at Scaffolding cornice. Because the depth of penetra- bracket and fascia locations where loss tion of the bracket units into the backup The aerial scaffolding erected during the of material had occurred. masonry could not be verified by non- initial survey at the southeast and south- The second part of the project in- invasive means, it was decided to an- west corners of the building provided a chor all brackets which had lost their vunoiltvsedhatvhiengstcabrialcikzeadtioinntoefrntaelrrwaebcosttaand, stable platform from which to work on outer scrolls or which had cracked inter- the cornice. Unfortunately, the expense also, those units susceptible to such nal webs. Given the condition of the and the disruption caused to the building cracking or displacement due to the an- light weight fill, this could only be tenants during installation of the scaf- ticipated slow, yet continuing, oxidation achieved by extending vertical anchors folding precluded the use of this type of of the steel structure and anchorages of through the roof (seefigure 5). scaffolding along the rest of the cornice. Frame-type scaffolding was also rejected as being too costly, given the height of the building. STEELDOG The use of swing-stage scaffolds proved to be a practical solution. To accommodate the tall projecting cornice, custom-fabricated brackets were made which permitted two swing-stage scaffolds to be hung side by side, parallel to and at a distance of about 2' out from the exterior wall. By tying the swing stages together and to the building, a BRASS EXPANSION ASSEMBLY stable work platform was provided for both the architect's detailed analysis of the cornice as well as the subsequent re- NEW7/ie" STAINLESS pair work (seefigure 8). A narrow sec- STEEL MECHANICAL ANCHOR SET IN DRILLED tion of scaffolding placed on the deck of SHAFTTHROUGH MORTAR the swings allowed for work on the up- JOINTBETWEEN FASCIA per reaches of the cornice. Using 32' UNITS long swings, roughly 10 drops were required, with l'/2 days of breakdown NEW%"x3V?"x4" and setup time between drops. Two sets STAINLESS STEEL ANGLE of double swings were employed for the job. New Anchor Holes To avoid introducing more water into NEWSTAINLESS STEEL TERRACOTTA NUTAND BEVELED the interior of the cornice, drilling of BRACKET WASHER ASSEMBLY the anchor holes was accomplished using air-cooled, rather than water-cooled, 1" diameter diamond core bits. These special bits have polycrystallized dia- Figure6. Detail section through the fascia ofthe corniceshowing the installation ofa fascia clip- mond (PCD) tips which are cultured angleanchor. Clip-angles were placed in thejoints between fascia units—128 total. Drawing by onto carbide teeth. High heat-resistant Jeffrey S. Levine. steel tubing is used near the head of the bit to prevent the diamonds from over NOTE: TYPICALDENTIL ELEVATION IS SHOWN BELOW. ANCHOR PLACE- MENTFOR OTHER UNITSHAPES TO BE DETERMINED INTHE I—EXISTING MASONRY FIELD BYTHEARCHITECT. EXISTINGTERRA BACKUP DENTIL COTTA UNIT NEWSTAINLESS ASTNEGELLEDRODDOWNWARD w\\\1 NEWSTAINLESS STEEL xwwwxx^ MECHANICALANCHOR SET IN 1" DRILLED SHAFT. INSTALLANCHOR WITH DOWNWARDANGLE IN UNITS WHICHARE SHELTERED FROMTHE WEATHER AND HORIZONTALLY IN EXPOSED UNITS NEWEPOXY PLUG, SCREED FLUSH EXISTINGTERRA VaW, 2" MIN W, 2" MIN. TO FACE OFTERRA COTTAUNIT COTTA.WROD IS COUNTER W SUNK MAX. Figure 7. The typical terra cotta anchor detail is shown here for a dentil unit. Other terra cotta units with cracked internal webs were anchored in a similarfashion. Roughly 30% ofall terra cotta units, exclusive ofthe brackets, were anchored in this manner. Drawing by Jeffrey S. Levine. r 4 4 A A 1 • ill ! Figure 8. Access tothecornice was provided by cantilevered aerial scaffolds at the southeastand southwest corners ofthe cornice. All other locations wereaccessed by hanging two swingstages, side by side. The inner swingwas hungoffofa V-shaped bracket (shown) while the outer swing was hung from a steel deadman which projected horizontally across the cornice roof. Both the V-shaped bracket and the deadman were designed to transfer the weight oftheswings vertically down through the center ofthe cornice. No load was placed on the outeredge ofthe cornice. Photos by Jeffrey S. Levine. heating and breaking loose. A 7/s" di- with stainless steel nuts placed at each ameter drill bit extension was used to end of the rod. Ultraviolet-protected allow for holes to be drilled deeper than neoprene pads and a paint coating on the 14" length of the bit. Air-cooled dia- the aluminum bearing plate were used to mond bits were also used to drill 2" di- isolate the aluminum and stainless steel ameter countersink holes in the face of components of the anchor assembly, the terra cotta units. TheWlast 3" of each thereby preventing galvanic action be- hole were drilled using diameter tween the two metals. carbide bits to accommodate the 7/i6" Stainless steel mechanical anchors, diameter expansion assembly at the end 7/i6" in diameter and with bronze ex- of the mechanical anchors. pansion assemblies, were employed for Drilling of the vertical and angled most other anchoring needs (seefigure bracket anchors was accomplished using 10). Anchors of various lengths were a drilling jig custom-fabricated out of special ordered from the manufacturer. lA" aluminum plate. The jig slid on The specified lengths were established tracks mounted on the roof deck and on in the planning phase by drilling test the wall of the building, just below the holes in the cornice at what were cornice (seefigure 9). All other holes thought to be typical anchoring loca- were aligned and hand drilled by skilled tions. A variable length anchor was also mechanics. developed for use in unanticipated locations and in areas of the cornice where Anchoring the original construction differed materi- Tplwooyedg,enoernaelftoyrpethseovferatnicchalorbsrawcekreeteanm-- awlelryefcroonmduthceteadre(aseienfwihgiurceh1t0e)s.t borings Fthiegucroern9i.ceD,riilnliangva6r'ieltoyngofvemrattiecrailahlosl,eswatshraough chors and one for the remaining anchor- As it turned out, the cornice construc- delicateoperation requiring great skill and ing needs. Vertical bracket anchors tion was not very consistent and anchor specialized drillingequipment. The aluminum ctohnrseiasdteeddsotfaianl6e'sslsotnege,l 7r/oi6d"wdiitahmeateVri" ptiloanceomfecnrtacvkasr.ieAdsacscooorndiansgthteo tinhietilaloca- dnarneigelldleeidndgbtjroiagdcrpkirelotlvtaihndecehdhoortlshe.espfDrorericltilhsieengavoelrfitgaincmavleerntatincdal thick, 4" square stainless steel plate order of fixed length anchors was used anchor is shown. To create an angled outer bearing on the roof deck and a XA" up, the drilling crew resorted to using scroll anchor hole, the drill was mountedon thick, 2" x 8" aluminum plate, bearing all variable length anchors since these the angled portion ofthejig, which passed against the underside of the bracket (see could easily be cut to the exact length dhiorleecstlcyouilndfbroentcoomfpltheetebdraicnke1t5.-3H0anmdi-ndurtielsl,ed figure 5). Aluminum was chosen over required for any given situation (see dependingon the depth ofthe hole and the type other metals for the bottom plate be- figure 11). ofbackup material encountered (e.g., brick, cetxawiuosstediinirgteccbtoriauoclnkdsetbt.eoTfmihotertehreoedparsaoifnliydlebbeeonaftritinhneg esiotnThrheyrebimnaectckhhueapnsitoecfeallthseatrncucochrtonurirsceec.ooruAtlnhdcehbomerai-snetg tdtmreoiironlrkulatetedcisomw,teitaatt,sholatsilhegiethgtjtni-hmgweeernijetgiqghuwtiiancrsoetndhmceormerpoterreo,ecpresittrtieimecplea)o,l.si3aHt0nio-dol6ne0.ist plate assembly was secured in place to steel was much preferred due to the Photo by Jeffrey S. Levine. unknown condition of the masonry backup. Pull-out tests were conducted on a large random sample of installed anchors. Utilizing a safety factor of four, very few anchors failed. Those that did fail had been anchored into masonry backup and were easily replaced after drilling deeper into the backup material. Project Evaluation The repair and stabilization of the terra cotta cornice of the Land Title Building was a large and lengthy project for the owners. The scope of the project could have been reduced, perhaps significantly, if timely maintenance activities, such as the replacement of the cornice's roof membrane, had been undertaken sooner by previous owners of the building. Working together, the owner, architect and PHPC achieved a repair ap- proach that maintains the integrity of the cornice as an integral feature of a land- mark building while simultaneously sat- isfying life-safety concerns and budget- Figure 10. A standard mechanical anchor (top) and a variable length mechanical anchor. The ary constraints. The drilling company's variablelength anchors were fabricated from 6' long threaded stainlesssteel rods, which were specialized equipment, skill, and close tapped at both ends to receiveexpansion assemblies (two anchorscould becut from each rod). working relationship with the architect Figure 11. Completed anchor installationsat afascia and bracket. Thecountersink holes penetrate no more than halfthe thicknessoftheouterwall of theterracotta and were filled later with epoxy. likewise contributed to the success of PROJECT DATA Structure 3 1604 011 831 411 the project. Joseph Cooke No changes were made to the original Building: Cooke-Chachkes, Consulting Engineers design of the cornice. Anchor assem- Land Title Building Philadelphia, Pennsylvania blies visible on the face of the cornice 100 South Broad Street from up-close are imperceptible from Philadelphia, Pennsylvania Contractor: street level. Further, none of the stabili- Joseph Dugan, Inc. zation repairs precludes the future resto- Owner: Erdenheim, Pennsylvania ration of missing elements. Although LTB Limited Partnership the very nature of terra cotta makes it A Pennsylvania limited partnership Drilling Contractor: impossible to guarantee the absolute in- Commercial Coring and Sawing tegrity of each masonry unit, the stabili- Property Manager: Vincentown, New Jersey zation program significantly reduced the Seneca/Roach Commercial Property potential for future loss of material. Services Anchor Supplier: Proper maintenance will help ensure this Philadelphia, Pennsylvania Dur-O-Wal, Inc. result. Baltimore, Maryland Architect: John Milner Associates Drill Bit Supplier: 309 North Matlack Street Golz Construction Tools West Chester, Pennsylvania Project Virginia Beach, Virginia Director: Neale Quenzel Project Conservator: Jeffrey Levine Project Date: 1989-1991 Easement Holding Organization: Project Cost: Philadelphia Historic Preservation The costs per lineal foot of cornice for Corporation water infiltration mitigation and 1616 Walnut Street stabilization of the terra cotta were $539 Philadelphia, Pennsylvania and $719 respectively. These costs exclude architectural, engineering, and building management fees. This PRESERVATION TECH NOTE was prepared by the National National Park Service policies, procedures and standards. This Park Service. Charles E. Fisher, Preservation Assistance Division, Tech Note was prepared pursuant to the National Historic National Park Service, serves as Technical Editor of the series. The Preservation Act Amendments of 1980 which direct the Secretary authors gratefully acknowledge the following individuals for their ofthe Interior to develop and make available to government review ofthis manuscript: John Hnedak, Mid-Atlantic Regional agencies and individuals information concerning professional Office, National Park Service; F. Neale Quenzel and Fred Walters, methods and techniques for the preservation ofhistoric properties. John Milner Associates; and Suzanna Barucco, Historic Comments on the usefulness ofthis information are welcomed and Preservation Planner. should be addressed to Tech Notes, Preservation Assistance Cover Photo: The Sansom Street tower from a 1905 post card. The Division, National Park Service, P.O. Box 37127, Washington, earlier tower is shown in the background at right. D.C. 20013-7127. This publication is not copyrighted and can be PRESERVATION TECH NOTES are designed to provide practical reproduced without penalty. Normal procedures for credit to the information on traditional and innovative techniques for author and the National Park Service are appreciated. successfully maintaining and preserving cultural resources. All techniques and practices described herein conform to established ISSN: 0741-9023 PTN-34 September 1991