antiquated structural systems series, part 10

7/24/2019 Antiquated Structural Systems Series, Part 10

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a i d s

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s t r u c t u r a l e n g i n e e r ’ s

t o o l b o x

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N O T E B O O K

STRUCTURE magazine January 201024

Antiquated Structural Systems SeriesPart 10

By D. Matthew Stuart, P.E., S.E., F. ASCE, SECB

This article includes a compilation ofmiscellaneous systems and informationfor use by the practicing engineer. Itis hoped that this final article – along

with the previous nine – has provideda resource of information to structuralengineers involved with the renovationof existing structural systems that arecapable of being adapted or reanalyzedfor safe reuse in the marketplace of todayand the future.

Additional AntiquatedSystemsMasonry

Masonry bearing walls were rarely, ifever, designed for actual loading conditions.However, analysis of a typical 8-inch,double-wythe brick wall for a three- tofive-story building indicates that thecompressive stresses are well below the al-lowable values that were common in the20th Century.

Building codes in New York City first addressedmasonry walls in 1830. Thecode provisions for brickbecame more complicated

with each revision and, by1892, the portion of thecode dealing with masonry

was its most complex part. The NYCcode, like many other codes from differentmajor cities, specified the minimum wallthickness for varying heights of buildings.

The 1892 NYC code generally called foran increase of 4 inches (i.e., one wytheof brick) in wall thickness for each 15feet down from the top of the building.The minimum thickness for “curtain”masonry brick walls was generally 4inches less than that required for load-bearing walls at the same height of thebuilding. As it is sometimes difficult toascertain the thickness of brick masonry

walls in existing buildings, a listing ofthe various minimum wall thicknesses

is provided here (Table 1, page

26 ) for a number of majorcities from the 1920s.Load-bearing brick masonry

walls were eventually replacedby cage and skeleton wroughtiron and steel frame con-struction, often using cast ironcolumns. Cage constructioninvolved the use of brick façade

walls that were as thick as thoseused for load-bearing construc-tion; the only difference wasthat the frame and supportingcolumns, including those that

would eventually be embeddedin the brick masonry façade

wall, were first erected ahead ofthe masonry. Skeleton framing,

although partially embedded in the extemasonry walls, was only clad with wamounted to a brick curtain wall. All thof these forms of construction co-exis

between 1880 and 1900.

Floor Framing

Draped mesh slabs became popularthe 1920s. Draped mesh constructis a type of reinforced slab framing tinvolves the use of wires that drape betwthe tops of adjacent beams. The typesmesh used included triangular wire mordinary wire mesh, expanded msheets, plain round and square rods twisted square rods. The use of wire m

was actually preceded by expanded m

sheets. Welding of wires together to fothe mesh did not begin until the 193Prior to that, the wires were attachat the intersection points by staples

washers, or by wrapping the transv wires around the longitudinal wires.

In a draped mesh slab, the concrserves only as the wear surface and as mechanism by which the imposed loare transmitted to the mesh. The malone is what physically spans betwthe beams by means of catenary actiBecause the concrete is not structur

stressed in this type of system, the coposition and quality of the concrete is as important as in a true flexural slab. Aresult, it was common to use cinder ccrete with compressive strengths un

Wainwright Building (St. Louis, Mo.). Example of steelskeleton framing clad with brick masonry.

Draped Mesh Floor.

For this series of articles, “antiquated” has been defined as meaning outmoded or discarded for reasons of age. In reality, however, most of the systems that have been discussed areno longer in use simply because they have been replaced by more innovative or moreeconomical methods of construction.

Web Resources Additional information concerning draped mesh construction can be founin the Practice Points archive of The Association for Preservation Technolo

website. www.apti.org/publications/PP-archive/Friedman-PPs.pdf


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Brick arch floor construction consisted ofa single arch of unmortared brick, typicallyonly one wythe or 4 inches thick, capableof spanning 4 to 8 feet with a center rise ofapproximately ⅛ of the span. The springline of the arch was constructed on top ofthe bottom flange of the supporting beams.The space above the arch was filled in withconcrete, which sometimes had wood nailerstrips embedded in the top of the slab. Tie rodswere commonly placed about⅓ of the heightof the beam and were spaced from 4 to 6 feeton center. The entire system had to be builton formwork, which supported the brick. Thethrust (T) on the arch, in pounds per linearfoot, can be calculated as follows:

T = (1.5 x W x L2

)/R Where: W = load on the arch in PSFL = span length of the arch in feetR = rise of the arch in inches

Other common floor systems included:Fawcett System and Acme Floor-Arch –

clay lateral cylindrical tile flat-endconstruction arch.Rapp Floor and McCabe Floor – gauge-steel

inverted tees spaced at approximately 8inches on center, supporting a layer of brickand upper cinder concrete slab spanning 4feet between supporting beams.

BRICK FLOOR-ARCH

CONCRETE FINISHED FLOOR

TYPE (A)TYPE (B)

TIE RODTERRA-COTTASKEW-BACKFLANGE PROTECTION

WITHOUT SKEW-BACKFLANGE PROTECTION

Brick Arch Floor.

The Kahn System.

A series of deformed bars.

Roebling Floor Arch – arch of dense wiremesh supported on the top of the bottomflanges of the beams covered with concrete. Manhattan System and Expanded MetalCompany (EMC) Floor – flat and arched(for EMC) expanded metal mesh covered

with concrete. Multiplex Steel-Plate, Buckeye and PencoydCorrugated Floor – Riveted steel platessupporting a concrete slab.Thompson Floor – Unreinforced concrete

slab spanning approximately 3.5 feet betweenbeams connected with tie rods.Roebling Flat Slab Floor and Columbian Floor

System – reinforced concrete slab. Metropolitan System – early draped meshfloor system.Plain round and square bars were typically

used in reinforced concrete buildings builtbefore 1920. Plain bars began to be phased outduring the 1910s and early 1920s in favor ofdeformed bars. The two types of deformationsused at that time included longitudinal andradial deformations. In addition, the Ransomebar included deformations induced by twistingsquare bars.Other forms of longitudinally deformed bars

included: the Thatcher bar, which was a square

bar with cross-shaped deformations on eface; the Lug bar, which was a square bar wsmall round projections at the corners; Inland bar, which was a square bar with raistars on each face; the Herringbone, Monotand Elcannes bars, which included compcross-sections similar to radial deformbars, but with longitudinal deformatiothe Havemeyer bar, which included rousquare and flat cross-sections with diamoplate-type deformations; the Rib bar, whincluded a hexagonal cross-section with cshaped deformations; the American bar wsquare and round cross-sections and lcircumferential depressions; the Scofield

with an oval cross-section and discontinucircumferential ribs; the Corrugated bar w

flat, round and square cross-sections wcup deformations; the Slant bar with a cross-section and low projecting diagonal on the flat faces; the Cup bar with a roucross-section and cup deformations; and Diamond bar with a round cross-sectand low circumferential ribs. The moddesignation of #3 to #8 round cup or diamodeformed bars was established in 1924.Reinforcing for concrete beams was also av

able in prefabricated trussed bar units. A tr

1,000 psi. The use of cinder concrete, how-ever, due to the acidic nature of the clinker(coal cinder) used as the aggregate, resulted inthe corrosion of the embedded iron beams andreinforcing mesh. Catenary systems are alsovulnerable to collapse as a result of failure ofthe wire anchorages.



bar is essentially a top bar at the ends of a beamthat is bent diagonally down to a bottom barposition at midspan. Prefabricated assembliesincluded the Kahn System, the CummingSystem, the Corr System, the HennebiqueSystem, the Pin-Connected System, the LutenTruss and the Xpantruss System.

ConclusionsEngineers involved with renovation and re-

habilitation projects need to be aware of thespecifics of antiquated structural systems inorder to develop non-destructive and unob-trusive solutions. This approach enables theproject to be more economically viable becauseof the extent of structural costs associated witha typical renovation project. In other words,without any knowledge of an existing structuralsystem, it is still possible to develop a structuralsolution; however, this approach will alwaysbe much more intrusive, and therefore morecostly, than if the engineer has a sound under-standing of the system involved.

Information concerning antiquated structuralsystems provided by this series of articles, andthe referenced source material, has been com-piled and made available because the historyof structural systems is far less documentedthan the history of architecture. This lack ofdocumentation can be traced to the generalpublic’s lack of awareness about the hiddenstructural components of a building, whichare typically enclosed after erection by thearchitectural finishes and therefore of less in-terest to a casual observer.This general lack of readily available in-

formation on antiquated structural systemshas occurred despite the fact that most of themethods of analysis and materials used in thiscountry, including steel and concrete, are notmuch older than 100 years. At the same timethat new materials, technologies and methodsof analysis have become available and readilyembraced by design engineers and the con-struction industry, previously used systemswere, more often than not, quickly discardedand forgotten.The information that has been presented

in this series is intended to represent the

knowledge that has been available at variousstages of different methods of constructionover the past century or so in the UnitedStates. However, this information cannot beused from a perspective in which any framingsystem can be assumed to correspond preciselyto a specific system described in the materialpresented. As is still the case now, the fact thatrecords indicate that a particular structuralcomponent should be able to support a givenload does not mean that errors were not madeduring the original construction or as a part ofthe initial design.

TotalStories

City Floor

1st 2nd 3rd 4th 5th 6th 7th 8th

2 Boston 12 12

New York 12 12

Chicago 12 12

Philadelphia 13 13

Denver 12 12

San Francisco 17 13

3 Boston 12 12 12

New York 16 16 12

Chicago 16 12 12

Philadelphia 18 13 13

Denver 16 12 12

San Francisco 17 17 13

4 Boston 16 12 12 12

New York 16 16 16 12

Chicago 20 16 16 12

Philadelphia 18 18 13 13

Denver 16 16 12 12

San Francisco 17 17 17 13

5 Boston 16 16 12 12 12

New York 20 16 16 16 16

Chicago 20 20 16 16 16

Philadelphia 22 18 18 13 13

Denver 20 20 16 16 12San Francisco 21 17 17 17 13

6 Boston 16 16 16 12 12 12

New York 24 20 20 16 16 16

Chicago 20 20 20 16 16 16

Philadelphia 22 22 18 18 13 13

Denver 20 20 20 16 16 12

San Francisco 21 21 17 17 17 13

7 Boston 20 16 16 16 12 12 12

New York 28 24 24 20 20 16 16

Chicago 20 20 20 20 16 16 16

Philadelphia 26 22 22 18 18 13 13

Denver 24 20 20 20 16 16 12

8 Boston 20 20 16 16 16 12 12 12

New York 32 28 24 24 20 20 16 16

Chicago 24 24 20 20 20 16 16 16

Philadelphia 26 26 22 22 18 18 13 13

Denver 24 24 20 20 20 16 16 12

Table 1: Minimum Building Code Thickness of Brick Masonry Walls – Inches.



In addition, it is common to encountersome overlap between a previous and morerecent method of construction, which has

resulted in a blending of two otherwise discretestructural systems. Also, before ASTM beganto standardize construction materials in thelate 1890s, the quality of irons, steels andcementious products varied greatly. Therefore,when dealing with a building that predatesASTM testing, samples of the existing structuralmaterials should be obtained and tested as apart of the due diligence effort.In the absence of existing drawings, the

methods of evaluating the properties of anexisting system include core samples forcementious material strength, depth and/or

thickness; coupons to determine iron or steeltensile strength; x-rays to determine internalreinforcement; petrographic analysis to deter-mine the quality, condition and consistencyof concrete; ground-penetrating radar (GPR);profometer to determine the location of internalreinforcement; Schmidt hammer to determinein situ concrete compressive strength; explor-atory demolition; and in situ load tests.In some instances, it is not possible or not

practical to obtain material strength propertiesof an existing system in order to complete ananalysis using current methods. However, if

the past performance of the structure has beengood (i.e., no signs of distress or significantdeterioration), then it is very likely that thesystem is adequate for the same use in thefuture. In such situations, however, it is helpfulto try and determine what the likely originallive load designation was for comparison tothe planned current use.If the engineer can determine what the likely

original use of the building was and has accessto copies of older building codes, it is some-times possible to determine the original live

Minimum Building Code Live Load - PSF

Building Type New York Philadelphia Boston Chicago Denver San Francis

1927 1929 1926 1928 1927 1928

Residential 40 40 50 40 40 & 60 40

Hotels, Hospitals 40 40 50 40 90 40

Office Buildings:

First Floor 100 100 125 125 125 125

Upper Floors 60 60 60 40 70 & 90 40

Classrooms 75 50 50 75 75 75

Public Seating:

Fixed Seats 100 60 100 75 90 75

Without Fixed Seats 100 100 100 125 120 125

Garages:

Public 120 100 150 100 150 100

Private 120 100 75 100 150 100

Warehouses 120 150 125-250

125-250

200 125-250

Manufacturing:

Heavy 120 200 250 250 250 250

Light 120 120 125 125 120 125

Stores:

Wholesale 120 110 250 250 120 125

Retail 120 110 125 125 120 100

Sidewalks 300 120 250 150 150 150

Table 2.

27

19 th Century Train Station (Reading Terminal,Philadelphia, PA).

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D. Matthew Stuart, P.E., S.E., F. ASCE,SECB is licensed in 20 states. Mattcurrently works as a Senior Project Managat the main office of CMX located in New

Jersey. Mr. Stuart may be contacted [email protected].

load for comparison to the proposed adaptivereuse. Individual building codes were com-monly developed by different cities before the

advent of national codes. These local codesoften reflected different allowable strengthsfor the same building materials and varyingdegrees of minimum live loads. Table 2 (page27) is an example of minimum live loads for anumber of major cities.The original criteria for the design of antiquated

structural systems was a performance-based ap-proach grounded in experience, both good andbad (i.e., successes and failures). The transitionto the more recent analytical design approachhas come about through the development ofstrength-based formulas derived from scientific

experimentation and tests. Structural engi-

neering of buildings as a separate disciplinedid not exist as late as the 1840s. However,the need for engineers began to grow in the

1850s with the advent of wrought iron beams, which had to be mathematically designed be-cause there was no craft tradition to providerules of thumb. In addition, the establishmentof ASCE in 1852 helped to promote the rapidspread of technical information, such as re-cords of experiments with cast and wroughtiron performed in England by Hodgkinsonand Fairbairn.It should also be recognized that an existing

structural system can often be found to havetwo different load-carrying capacities – onefound using the original codes and methods

of analysis, and another using the currentcodes and methods of analysis. The differencesbetween these two approaches can typically beexplained by the expansion of knowledge inthe field of structural engineering. More oftenthan not, comparisons between the originaland more current methods of analysis willreveal that the older design was conservative.In any case, if the properties of the materialscan be substantiated, it is always possible toanalyze an older structure using the latestmethods of analysis and most current codes.In most cases, in fact, the current building

code will mandate such an approach.In situations in which it is confirmed that

the existing structural system does not havesufficient capacity to support the new loads,there are two basic methods that can be usedto rectify the condition: adding new framingmembers, either to support the new loads inde-pendently or to provide supplemental supportof the existing structure; and/or internally orexternally reinforcing the existing system.▪

GPR printout.

Current Day, Jim Thorpe, PA. Strengthening of existing slab (Slag Block System).

28

Early 20 th Century Retail Arcade (DowntownNashville Arcade).

Reference Material Architects’ and Builders’ Handbook, 18th Edition, Frank E. Kidder, Harry Parker, Jo

Wiley and Sons, 1956

Historical Building Construction, DonaldFriedman, W. W. Norton & Company, 19

Structural Engineers’ Handbook, MiloS. Ketchum, C.E., McGraw-Hill BookCompany, Inc., Second Edition, 1918

antiquated structural systems series, part 10

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