B09_-_Attachment_1_-_Merchants_Exchange_vol_1_INDE_391_D311_-_Amend_0001_0001.pdf

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VII cC

A CASE HISTORY COMMENTARY

MERCHANTS EXCHANGE BUILDING

INDEPENDENCE NATIONAL

HISTORICAL PARK

PHILADELPHIA PA

PART ONE

November 10 2005

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TECHNICAL INFORMATION CENTER

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K EAST HOOD CO

Structural Engineers

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Photo by Jeff Totaro

William Strickland Architect and Engineer Constructed 18321834

A CASE HISTORY COMMENTARY

MERCHANTS EXCHANGE BUILDING

INDEPENDENCE NATIONAL HISTORICAL PARK

PHILADELPHIA PA

PART ONE

KEAST HOOD CO STRUCTURAL ENGINEERS

PHILADELPHIA PA

KHK

A CASE HISTORY COMMENTARY

MERCHANTS EXCHANGE BUILDING

INDEPENDENCE NATIONAL HISTORICAL PARK

PHILADELPHIA PA

PART ONE

Summary Statement of

Structural Condition Assessments for Adaptive Reuse

Keast Hood Co Structural Engineers

Philadelphia PA

November 10 2005

10 General and Early History

11 Keast Hood Co were retained in 1994 to be the prime design professional for the structural rehabilitation of the Merchants Exchange Building The work to be performed was to be in two phases toward the adaptive reuse of the historic building designed and constructed by William Strickland in 183234 An extensive condition assessment of the buildings structure by this office preceded the initial phase of the adaptive reuse Stricklands interior construction had been replaced in 1902 by one of structure steel with flat terra cotta arch floor slabs It was determined during the condition assessment that the 1902 steel framework and foundations could be retained but that the terra cotta floor slabs with their heavy concrete fills had to be replaced with lighter weight contemporary office floor construction An extensive geotechnical investigation confirmed that the existing 1902 mass concrete footings could be reused The investigation also disclosed that the buildings original exterior foundation walls had been underpinned in 1902 to provide a basement of sufficient height for cold storage rooms Where new infill floor construction was added to the building in 1997 and where the existing foundations were inadequate new foundations incorporating high capacity minipiles were provided The second phase for the adaptive reuse was to be the architectural and building services fitout with design services being provided by the Denver Service Center DSC of the

National Park Service The contractor for both phases was the Daniel J Keating

Company

12 The chronology of physical changes to the buildings original construction in 1902 included the total removal of its interior brick vaults masonry walls and timber floors These were replaced with a then stateoftheart steel structure supported by new stepped mass concrete footings In 1922 significant infill floor construction of some interior open spaces was added for additional office space In 1958 further interior modifications with limited floor additions were completed to prepare the

Iffl KEASTHOODCO A Case History Commentary 11110+05

Merchants Exchange Building Page 2

Independence National Historical Park

Philadelphia PA

Part One building for occupancy by the Eastern Office of Design and Construction EODC of the NPS The 19952002 double phased project led to the buildings becoming the new centralized headquarters for the Independence National Historical Park INHP

1 3 The building was designed by William Strickland the Philadelphia architect and engineer considered by many to be the father of the Greek Revival Style of architecture in the United States Other buildings designed by him in Philadelphia included the Second Bank of the United States Independence Hall Tower and the

Philadelphia Naval Home The Exchange Building was the last significant commission completed by Strickland in Philadelphia before journeying to Nashville to design the Tennessee State Capitol Building Although Strickland experimented with various revival styles there was conceptual design continuity through his many Greek Revival commissions The structure of the Merchants Exchange Building was typical of other early 19`x century institutional buildings constructed in Philadelphia where exterior and interior bearing walls were of masonry The exterior wall of the building was a composite of Pennsylvania Marble facing bonded to brick backup while the interior bearing walls were of brick The marble used is technically a higher grade limestone from nearby quarries which does not have the weathering resistance typical of true marbles The buildings marble exterior as well as others within INHP have suffered considerable surface degradation ie delamination from atmospheric pollutants and have been the subject of ongoing conservation studies by the NPS The University of Pennsylvanias Department of Historic Preservation recently conducted a study for the NPS to assess the cause for the materials deterioration and the potential treatments for its consolidation Keast Hood Cos services were not a part of the conservation study pursued by the University of

Pennsylvania

14 It was determined early that the foundation walls were constructed of schist rubble supported by the silty sands common to most of the Independence National Historic

Park INHP buildings Such soil is known to support the Independence Square buildings Philosophical and Benjamin Franklin Halls of the American Philosophical

Society APS Franklin Court Christ Church and Carpenters Hall The competency of the soils support capacity can be illustrated by Christ Church Tower where the bearing pressure exceeds 11 ksf It is apparent at that site from brick repair evidence at the juncture between the tower and the west wall of the Church that early soil consolidation was followed by a long period of stability The aforementioned buildings and others located in the central eastern portion of the city have been provided professional consultation services by Keast Hood Co since the early

1960s

A Case History Commentary

Merchants Exchange Building

Independence National Historical Park

Philadelphia PA Part One

Ili 1005

15 The 1902 comprehensive adaptive reuse of the building included the replacement of the interior floors and the roof construction It is this offices opinion based upon limited evidence visible on the foundation walls that the first floor was historically supported by brick vaults and that the second third attic floors and roof were of timber construction The presence of joist pockets on some interior faces of the backup brick as well as 1901 demolition photography confirms the prior existence of such construction The roof construction had most likely included timber trusses with purlins and rafters There is limited evidence of there having been timber roof trusses by the presence of two end remenets embedded in the fourth floors upper walls

With respect to the foundation walls there are continuous integral inclined masonry bearing haunches along the exterior basement perimeter walls for the seating of the brick vaults Strickland made extensive use of groined brick vaults for the earlier

Second Bank of the United States on Chestnut Street in 1821 and demonstrated in that project his familiarity with such construction Its structure was probably the first fireproof building in Philadelphia The early two story extensions of Independence Hall connecting Congress Hall and City Hall by Robert Mills a contemporary of

Strickland also utilized fireproof brick masonry vaults Mills first floor vaults remain today to be seen in the service tunnels connecting the basements of the Independence group of buildings ie the State House with Congress and City Halls At the

Exchange Building there was no evidence of the size and placement of the interior brick bearing walls that presumably supported the brick vaults and the timber framed upper floors of the building

20 Exploratory Programs and Review Analyses

21 At the commencement of the project this office was provided with a complete set of the original 1902 structural engineering drawings prepared by Hickman the

Architect for the buildings first adaptive reuse These were to facilitate the review analysis of the existing construction with respect to the structures ability to support contemporary code conforming occupancy loads In retrospect it appears that the

NPS prior to the commencement of the project had assumed that the existing construction was adequate for a contemporary adaptive reuse except for some limited reconstruction or alterations Presumably their premise could have been that the extensive 1958 alteration documents constituted confirmation of the existing structures adaptability for alterations Unfortunately after inquiries the NPS acknowledged to having accidentally discarded their 1958 structural calculations rendering the validity of such a premise improvable The 1902 modern construction for the building consisted of steel framed floors and a roof supported by builtup steel columns bearing on stepped mass concrete unreinforced footings The infill floor system supported by the beam and girder framing was comprised of hollow 8 inch flat

A Case History Commentary l U1005 Merchants Exchange Building Page 4

Independence National Historical Park

Philadelphia PA

Part One terra cotta arch slabs originally topped with lightweight cinder concrete fills with embedded sleepers for the finish wood floors The comparative review of the 1902 documents and the 1958 EODC modifications disclosed that the present basement floor elevations differed substantially from those indicated on the 1902 drawings Cognizance of such posed concern for the condition of the then deeply embedded column bottoms which were in many cases more than three to eight feet below the

1958 floor elevations A request for the excavation exposure of three column bottoms to permit condition assessments for rust diminishment was met with skepticism and reluctance by the DSC Permission to eventually proceed was predicated upon the parallel discovery of the first floor framing above the basement being at considerable variance with the framing provided on the 1902 drawings Where 15 1 beams were indicated on the 1902 structural drawings 12 I beams of lesser weight at closer spacings had been provided Cores extracted from the floor slabs disclosed in some cases that concrete floor fills approaching 5 to 8 inches in thickness had been placed over the terracotta arches spanning between the floor beams thereby imposing significant dead loads onto the floor and column framing It is our premise that the weight reductions of the steel construction shown on the 1902 documents with respect to that found at the site were the consequence of some form of early value engineering

22 Exploratory pits excavated adjacent to randomly selected columns disclosed the existence of considerable crosssectional diminishment from rust of the brick encased buried column bottoms Also important was the disclosure that the composite columns were fabricated of smaller angle sections than scheduled on the drawings provided as the as built information for the first phase condition assessment As a consequence of the columns being both undersized and rust diminished the NPS was advised to pursue further pit explorations to assess the steel columns and the suitability of the foundations for sustaining contemporary occupancy loads The combined discovery of the 1902 structural drawing being at variance with the existing foundations and floor framing and that perched ground water levels were well above the bottom elevations of the 1902 footings led to amending the scope of structural services to be provided by the structural engineers As the site investigations progressed it was concluded that a contributing factor to the rusting of the embedded column bottoms was the low subgrade temperatures of the soils supporting the refrigeration rooms located throughout much of the basement

Although cork was employed to insulate the bottoms of the slabs on grade the walls ceiling and the column shafts the subgrade soils frequently froze from the condensed ground water vapor entrapped below the floor slabs supporting the refrigerated spaces above

FEH KEASTHOODCO

A Case History Commentary 1 1 10005

Merchants Exchange Building Page 5

Independence National Historical Park

Philadelphia PA Part One

23 The projects geotechnical exploratory program included soil test borings and the exposure of the 1902 stepped mass concrete footings and the 1902 brick underpinned exterior schist rubble walls It was discovered that the depths of the historic exterior wall bottoms and the 1902 underpinning varied along the buildings perimeter in response to the soil quality encountered during the original construction The better soils generally favored the west end of the building which were more distant from the influence of one of Dock Creeks tributaries which was located diagonally across the northeast corner of the building The east and northeast sides of the building were in closest proximity to the creek By explanation the creek was an estuary influenced by the tidal fluctations of the Delaware River and was not a free running creek as many have presumed Keast Hood Co fortunately possesses a rare set of 1932 PWA reference survey drawings which locate the streams and creeks within the city limits the larger of which had been channeled into conduits The maps confirmed that the estuary to the east of the building was sizable and extended towards Carpenters Hall and beyond In many cases during the 19` century estuaries creeks and streams were either contained within conduits or simply backfilled As foundations were required to support the new interior stairtower and new columns for the miscellaneous floor infills the perched ground water levels encountered at the exploratory pits adjacent to the 1902 footings confirmed the need for test borings to evaluate the soils that would support the new construction On the basis of the observed ground water elevations within the exploratory pits one surmises that the construction of the 1902 foundations and underpinning must have been fraught with difficulties as the consequence of the extensive pumping and sheeting required to protect the excavations To avoid such a reoccurrence it was decided earlyon through discussions with the geotechnical consultants that some type of deep foundations would be most appropriate to cope with the existing site conditions

24 The geotechnical program consequent of the discovery of perched water was pursued by URS Woodward Clyde under the guidance of Nasser Massoudi PE PhD who contributed much to the successful outcome of the project Their extended investigative report is Appendix D of Task Order 25 Modifications 3 4 and 5 Contract 1443XC200092036 dated June 7 1996 The Task Order Report also develops in detail the investigations relative to the assessment of the 1902 1922 and

1958 steel constructions which were subsequently determined to be suitable for incorporation into the improved building structure providing that the existing heavy slab system was replaced with contemporary lightweight construction

25 The investigations focused on the mutual ability of the existing mass concrete footings with their underlying soils to support the modified superstructure loads of the adaptive reuse To qualify the suitability of the 1902 concrete to sustain the new

A Case History Commentary 111005 Merchants Exchange Building Page 6

Independence National Historical Park

Philadelphia PA Part One column loads drilled cores were extracted from several footings and tested for compressive strength at the Pennoni Testing Laboratories The test results exceeded

3000 psi which was more than adequate for such type footings The removal of the terra cotta slabs with their heavy fills in exchange for a lighter composite metal deck system with lightweight concrete permitted superimposed live load capacities suitable for contemporary office occupancy Where the embedded steel column shafts below the first floor were discovered to be heavily rusted and undersized they were concrete encased and provided with shear connectors to transfer the column loads of the floors and roof above into the new concrete column encasements The concrete column encasements in turn transferred their loads onto new concrete plinths constructed over the stepped upper portion of the mass concrete footings The geotechnical feasibility of the concept focused upon limiting the increased dead load soil pressures of the individual footings beyond those which existed Also in consideration of thecrosssectionaldiminishment of the column shafts the most critical reductions were noted to have occurred at the earth embedded portions andor where the basement perimeter columns were engaged with the rubble foundation walls In those cases where the wall engaged flanges of the 1902 builtup columns had been severely diminished by rusting supplementary plate reinforcements were added prior to being encased with concrete

26 An investigative exploratory program was required to qualify whether the structural steel framing from the 1902 reconstruction could be retained for the adaptive reuse of the building The earlyon discovery that the existing framing differed radically from that shown in the 1902 drawings that the buried column bottoms were significantly rustdiminished and that perched ground water was going to impede the installation of new foundations qualified the need for extended investigations to confirm the validity of retaining and reincorporating the 1902 steel superstructure The initial programs were geotechnical to be followed by laboratory testing of steel specimens extracted from the framing incorporated to the three distinct periods of construction of 1902 1922 and in 1958

27 In those cases where new construction was required within the building which could not be supported by the existing footings drilledinplace minipiles were chosen to be the supplementary foundation system Test borings in conjunction with exploratory foundation pits had confirmed the presence of perched ground water above the bearings of the existing footings That condition would impede excavations for new conventional foundation footings bearing at the same elevations of the 1902 construction Construction access to suitable soils capable of supporting new conventional foundations would require dewatering and earth retention sheathing for protection of the excavations and nearby footings from being

A Case History Commentary 111005

Merchants Exchange Building Page 7

Independence National Historical Park

Philadelphia PA Part One undermined The minipile system chosen for the project utilized 6 inch id pipe with unit bearing values of 40 T each The piles were friction type with total embedded lengths of 45 feet which were determined by load testing a test pile The unit piles were designed by Dr Massoudi the project geotechnical consultant who also monitored and supervised the load testing of the test pile Refer to Plates 7 8 9 10 and 1 l for captioned illustrations qualifying the suitability of the 1902 stepped concrete footings and the installation and testing of the minipiles

30 An Unsatisfactory Investigative Procedure

31 Earlier in the project and pursuant to the initial exploratory exposure of the column bottoms and the discovery that the floor framing of the 1902 drawings differed from that observed in the building it was mutually agreed with the NPS to quickly pursue nondestructive procedures to qualify the framing arrangements The purpose for doing so was to avoid fracturing the early 201h century suspended plaster on metal lath ceilings known to contain asbestos To avoid exposure to the plasters asbestosnondestructive test techniques employing Impact Pulse Echo were selected to locate the concealed 1902 steel beams and the reinforcement of the 1922 and 1958 concrete slabs The tests were provided by Muenow and Associates from Charlotte NC who swept the floors with their sensing devices which proved to be ineffective for their intended purpose

32 The consultants qualification for the instruments failing to accurately locate the 1902 beams and of the 1958 slab reinforcement was wave interference With respect to the terra cotta its iron content shielded the beams from the wave emissions and in the case of the slab reinforcement of the 1958 infill construction the existing steel slab forms reflected echoes more prominently than those of the slab reinforcement As a consequence of the failed testing procedures the suspended ceilings were removed to expose the soffits of the terra cotta slabs and the girder encasements The beams were located their sizes determined and the combined weight of the terra cotta slabs with their concrete toppings calculated The plaster removal conformed to OSHAs asbestos abatement procedures

40 Investigations and Assessments of Superstructure

41 Scrutiny of the available structural drawings from the 1902 1922 and 1958 periods of construction posed consideration for the appropriate allowable flexural and compressive stresses to be used for the review analysis of the existing framing within the building It was determined that such information could logically be made by extracting samples of the material at the site and subjecting them to laboratory testing

KH KEASTHOODCO

A Case History Commentary 1111005

Merchants Exchange Building Page 8

Independence National Historical Park

Philadelphia PA

Part One

The samples were flamecut from the ends of identified beam flanges and then machined to ASTM conforming specimen configurations The specimens were than subjected to tensile tests to determine the mechanical properties of the three different periods of steel construction and metallurgical tests to qualify their suitability for welding

42 The review analysis which incorporated the known member properties and the existing construction weights disclosed that the existing steel from the three construction periods lacked the capacity to safely support contemporary office occupancy loads The conclusions were that the terra cotta flat arch slabs with their concrete toppings should be replaced with lightweight contemporary floor slabs and that the structural steel would be retained with supplementation or repairs as might be required

NACase StudiesNerchants ExchangeMerchants Exchange Part l i 1100>doc

A CASE HISTORY COMMENTARY

MERCHANTS EXCHANGE BUILDING

INDEPENDENCE NATIONAL HISTORICAL PARK

PHILADELPHIA PA

PART ONE

APPENDIX

PART ONE

PLATES

The sources for the plate illustrations were the following

Plate 1 Philadelphia Exchange no date George Strickland Delineator

J Sartain Engraver

Plate 2 Library of Congress

Plates 3 through 18 Keast Hood Co

FEll KEASTHOODCO

Plate 1 Mid 19 c view of east end from southeast with the First Bank of the United States beyond where Dock Creek meets Second Street

Plate 2 Rear west facade which was altered to become the front facade with the buildings main entry during Hickmans 1902 adaptive reuse program The 19981999 structural adaptive reuse of the building retained the historic exterior masonry walls with their foundations in conjunction with the interior 1902 structural steel framing with its stepped mass concrete footings Refer to

Plate 3 for a transverse crosssection through the building illustrating the extant framing and some of the subsequent remediations for the adaptive reuse

Plate 3 Transverse section from Drawing S7 Part 2 showing 1902 adaptive reuse structure

1958 roof renovations and 1998 modifications for new stair tower and reuse of 1902 structural steel frame including stepped mass concrete footings Cupola shown in Plates 2 and 3 was a

1958 replica of the original

Plate 4 Detail view of a marble Corinthian column capital from the west facade Capitals were sculpted from Italian Carrara marble while column shafts were of Pennsylvania marble

Sculptors names the Bardi brothers were incised into narrow ring juncture of column capital with shaft

IEH KEASTHOODCO

Plate 5 Floor is being swept by Impact Pulse Echo procedure to confirm beam locations of

1902 steel framing Procedure proved to be invalid by presence of high iron content in terra cotta flat arch tile units which distorted echo waves Failure of procedure required that the ceiling plaster below each floor be removed employing asbestos abatement procedures

Plate 6 Instrumentation required for recording pulse echo readings generated by sweeping shown in plate 5

Plate 7 Exploratory pit excavated adjacent to a 1902 stepped mass concrete footing which served to confirm footing configuration and condition to permit sampling of soils at footing bearing elevation High level perched ground water precluded use of conventional footings for support of new building columns as dewatering of footing excavations could initiate settlement of the existing foundations It can be seen from the wetness of the soil in Plate 7 that the perched ground water level was found to extend to the top of the foundation prior to dewatering of pit

Plate 8 Components for installing a typical 6 inch id minipile From left to right a drillbit for advancing a hole through soil Drillbit fits within and advances through lead casing positioned at right end of this photo Also shown at center of top row is a dragbit Threaded drill rods with internal and external threads at opposite ends when assembled advance the hole for the pile

Larger diameter pipe at right side is a lead casing note cutting shoes on bottom of casing

Completed pile includes a reinforced grout core Reinforcement consists of a single large diameter bar as shown in Plate 11

Plate 9 Tracked drilling rig shown installing a unit pile in basement of the Exchange Building Rig had been designed to cope with low overhead clearance Low clearance conditions require that pile be comprised of shorter pipe lengths

Plate 10 Load test of 40 ft long pile in progress Test setup requires that test load be resisted by two anchor piles one at each end of the steel load frame Test load is being applied by hydraulic jack at load frame center with deflections measured by dial gages Failure load of 40 ft test pile with a factor of safety of 20 qualified it to be a 35 ton unit By extending the lower bond zone of pile an additional 5 feet and drilling the casing into the top of the grout zone calculations qualified the pile for a 40 ton unit capacity The support of the new columns and the underpinning resupport of the existing elevator pit and shaft way required the installation of 17 40 ton minipiles Shown in photograph is Nasser Massoudi PE of the URS Corporation monitoring the progress of the load test The URS Corporation were the project geotechnical consultants

FEII KEASTHOODCO

Plate 11 Center reinforcement of a typical pile consisted of a No 18 bar Bar is shown with one of the strain gages used to assess internal stresses of the test pile Shown also at right is a bar splice coupler which facilitates the assemblage of shorter bar lengths as limited by overhead clearances into the required full length center reinforcement of a pile

Plate 12 Tensile test specimens used to determine mechanical properties of structural steel used in the 1902 1922 and 1958 phases of construction Specimens were machined from coupons burned from top flanges of selected beam ends Specimen preparation and testing conformed to ASTM A370

KEASTHOODCO

Plate 13 Illustrates demolition removal of 1902 terra cotta flat arch floor slabs of second floor

Project specifications limited demolition procedures to use of manual power tools to avoid damage to flanges of existing steel framing Temporary shoring platforms were provided between the basement first and second floors to limit the full impact of the demolition debris from above The removal of the heavy slab construction permitted the use of lightweight contemporary floor construction thereby gaining significant increase in superimposed live load capacity

Plate 14 An example of new supplementary infill framing of third floor Framing connections of new steel to old steel were combinations of weldments andor bolted details New floor slabs are of galvanized composite steel decks with lightweight structural concrete fills

IEH KEASTHOOD CO

Plate 15 A typical outofplumb condition found Plate 16 New concrete plinth being poured at many of the 1902 basement columns Out with normal weight concrete by means of ofplumb dimensions varied from 1 to 2 12 as pumped concrete Reinforcement for column shown in column illustrated New concrete encasement is not yet in place plinth at top of existing stepped concrete footing has not yet been poured All of the basement columns were strengthened by concrete encasements

KHKEASTHOODCO

Plate 17 Rust deteriorated column flange of existing basement column No 10 Deteriorated flange portions were burnt off and reinforced by plate weldments prior to being encased with reinforced concrete Short sections of C6 steel channel shear connectors were welded between column flanges to facilitate load transfer of floor and roof construction into the basement composite columns Refer to Plates 15 and 16 for other lower column conditions

FEll KEAST HOOD CO

Plate 18 Placement of lightweight concrete fill onto a composite steel deck Placement is by pumping New first second and third floors were supported by steel framing originating from the original 1902 adaptive reuse and the subsequent 1922 and 1956 infill renovations The 1902 columns and their soil bearing mass concrete footings were retained for reuse The bottom shafts of the existing columns were concrete encased Where new steel columns were required for the new infill floor construction or for the load relief of some existing construction new foundations utilizing 40 ton minipiles were provided t n i

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