Monitoring Building Response to Adjacent Construction

Monitoring Building Response to Adjacent Construction

By Charles J. Russo, P.E., Michael L. Brainerd, P.E., and Milan Vatovec, P.E., Ph.D.

®

R EFigure 1: Large-scale excavation with adjacent existCinogpbuyirlidginhgts and hardscape.
New construction projects in congested urban settings commonly require demolition of an existing structure and deep
excavation to accommodate several levels of below-grade parking or occupied space associated with the new building (Figures
T U1 and 2). The prediction and monitoring of building response to adjacent construction activities is necessary to minimize
building damage resulting from subsurface movement and ground-borne construction vibrations.
ePotential Impacts from foundation that needs to be extended happens if the size or depth of the new
Construction Issues downwards. Some vertical settlement, underpinning elements is not sufficient.
C inConstruction Activities potentially on the order of ¼ inch to Often underpinning piers are also part
discussion of construction issues and techniques ½ inch, should be expected as a result of the earth-retaining system. As with
The most common construction activi- of underpinning procedures, which in- other excavation support systems, their
clude excavation and transfer of loads to lateral movement can result in vertical
U zties associated with urban construction the typically continuous underpinning settlement of retained soils.
components. Larger vertical movement
projects and their potential impact on ad-can occur when widely-spaced intermit- Dewatering Operations
tent underpinning piers or intermittent
ajacent buildings are described below. underpinning piers with relatively flex- Deep excavations often require dewa-
ible interpier beams are used. Additional tering. Dewatering has the potential to
T R gExcavation Support Systems cause ground settlement, settlement of

aDeep excavations for urban construc-

tion require installation of temporary

S mearth supports, such as cantilevered
systems (sheet piles or soldier piles and vertical movement can also occur from pile foundations due to drawdown (nega-
timber lagging), anchored systems using settlement of the bearing strata beneath tive skin friction), or rotting of untreated
tiebacks, or strutted systems (cross-lot the underpinning piers. This typically wood pile foundation systems.
braces, corner braces, or raked braces).
continued on page 16
Inward deflection of earth-retaining

systems during excavation results in lateral

movement of existing soils outside the

excavation, as well as vertical settlement

of building components supported

on the shifting soil. The amount of

vertical settlement is dependent on the

flexibility of the earth-retaining system,

depth of excavation, type of soil, and

distance away from the excavation. The

variation of settlement with distance from

the excavation can cause differential

settlement of the building.

Underpinning Figure 2: Adjacent buildings and retained facade underpinned to permit excavation.

Foundations of existing buildings are
frequently underpinned to deeper bear-
ing strata to accommodate adjacent new
construction. A common method is
concrete pit underpinning, which typi-
cally involves sequential and phased
installation of simple concrete foundation
elements directly beneath the existing

STRUCTURE magazine 14 November 2008

Removing water from weaker, compressible

Simpson Strong-Tie® soil strata, such as soft clay, peat, and silt,
effectively increases the stress on the soil,

Design Tip which can cause consolidation. Depending
on the extent of compressible soils and the
profile of the water-elevation drawdown,

settlement can either be uniform or differ-

ential over the building footprint. On pile- ®
supported buildings, consolidation of soil
Introducing the value-added
moment-frame solution— around piles can create negative friction

™resulting in a downward force on the piles

Strong FrameOrdinary Moment Frame and subsequent settlement.

ngineered moment-frame solutions When sections of previously immersed,

E save time for the designer, but the untreated wood piles become exposed to

EStrong Frame moment frame has also air, conditions such as moisture and abun-

been designed to reduce the time and dacaraeyntcprroeoxacyteegCsdeso.naTp,nynhdreeicigrneahsittsetiaarotyef for fungal growth, Figure 3: Close-in construction operations.
cost associated with installation: an accelerated de-
Project Criteria
U C TziUneR100%field-boltedconnections: deterioration of piles

ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org afaster assembly and installation, no is highly sensitive to even minor variations The design professional should prepare
in the environment around the piles: wood performance-based contract requirements
welding or special inspection needed species, soil chemistry and makeup, etc. Con- in consideration of anticipated responses of
sequently, the duration of exposure necessary adjacent buildings during construction. An
T R gWood nailers are pre-installed on to significantly impair the structural integrity example is a performance-based specification
of timber piles is unpredictable, but is usu- for temporary earth support that outlines per-
athe frame: No more field-drilling and ally longer than the length of most temporary mitted systems, performance limitations on
construction-related dewatering operations. movement, and monitoring strategies. This
bolting of nailers

S mFrames fit in a standard 2x6 wall:

No thicker walls or furring required
Ground-borne Vibrations approach allows the contractor competitive
freedom to determine how to accomplish the
Ground-borne vibrations associated with construction, but maintains controls established
construction can cause architectural damage by the design professional, with the specific in-
to building components, such as interior tent to minimize damage to adjacent buildings.
finishes or exterior facades, structural damage, This approach requires that design profession-
and settlement or consolidation of loose fill als survey the condition of adjacent properties
supporting structures and utility services. Deep to understand their present condition and
foundation installation is a common activity fragility, establish acceptable response limits,
with potentially damaging vibrations associated conduct soil-structure analyses of various

Field adjustability to account for with driving, vibratory, or drilling (Figure 3) earth support systems and develop limits on
anchor-placement issues: Column to operations. In addition to the physical effects their respective movements (to be included in
beam connection can be shimmed ¾" on structures, ground-borne vibrations can be the performance-based specification), and de-

alarming and disruptive to building occupants velop a monitoring strategy.
and can disrupt vibration sensitive equipment. Design professionals establish thresholds
Different types of construction equipment and limiting criteria for the monitoring pro-
cause different types and levels of vibration; gram for each aspect of building response
selection of the appropriate construction (settlement, translation, rotation, and/or
approach is important when it comes to vibration). Thresholds and limiting criteria
vibration control and mitigation.
are safeguards established for each adjacent

Demolition Activities structure based on age and type of construc-
tion, condition of the building, and perceived

Although typically not anticipated to affect sensitivity of the building to movements. In

Pre-assembled anchor bolt adjacent buildings when done carefully and establishing thresholds and limiting criteria
assemblies: Easy to layout and rraeecTdTsstohopuivacoleitnunntikmsseiinuysberonlecyudta,t,anfhfimodalrlateaorlmgtetuheevtoe.rietlpihAwetrxeidoioinisdpnngtieiftnotriahorgacmindstsaivaavuletdlipiyrtot,ippeinsorsdoebremotecmflaesofnyonowsltrittfaetaoihmnlosrednosyufoapuxcrtfcoictoioomotrnnomisvniupoidgsbaceranicrsatuyst:rutii6oshse0naraout8st,fn-5Shl,dep2Tuve4lRmese-ilUags4asCnn4emT3ppUu2prrc.ReionhrEfcte®eloseMpsusitsotaiogntthnhaailazssnionfnene.veeeidbdretado-
attach to the form for remaining adjacent buildings. This is for damage, and that adjacent buildings
For more information call (800) 999-5099 often tYhees,ctahseeawdhloeonksa fibnuei.lding on one side might house tenants working with vibra-
or visit www.strongtie.com.

of the party wall is demolished, rendering an tion-sensitive equipment. When a criterion

inadeqNuaot,eweorecqoumireptrhoemfiosleldowliantgercahl abnrgaecsin: g of building response is reached or exceeded,

support for the remaining party wall. Such the contractor will be required to implement

situations require immediate (temporary) a mitigation program, which may include

stabilization measures (Figure 4, page 18). alteration of the excavation/construction

©2008 Simpson Strong-Tie Company Inc. SFSTIP08 If we recieve no fax within 48 hours of this email, wapepwroilalcahs,suinmteentshiafitetdhmereonisitnooricnhgatnogeallow for
necessary and will run the ad as presented here.Thank you for your assistancocne.tinued on page 18

STRUCTURE magazine 16 November 2008

a timely response, or, in extreme cases, The workhorse of a monitoring pro-

stabilization and shoring of already gram is a total station. A total station is

damaged building components. A well- a versatile piece of equipment that al-

defined set of criteria and an up-front lows high-accuracy, long-distance, and

agreement between all involved parties angular measurements, by producing

goes a long way towards avoiding con- 3D positioning records of monitoring

struction delays and damage claims. points. Most equipment use reflecting

Quite often, design professionals are prisms as targets mounted to a bui®lding.

not retained for these services. In such Some have reflectorless capabilities that
Ethe earth support system accordingly, use a visible red laser to site a feature of
cases, responsibility to monitor and the structure. A significant amount of
data can be electronically collected in a
protect adjacent structures is allocated to relatively short time. Also, a macro can
and develop a monitoring strategy. be created in a template spreadsheet to
extract collected data and process infor-
RA loosely-defined performance-based mation automatically into tabular form
the contractor. Under this scenario, the and trend-line plots.

contractor and their specialty structural Data captured by the 3D positioning
system is primarily used to evaluate vertical
engineer need to establish acceptable movement for settlement and horizontal
T Usimilar to “design, furnish, install, monitor, extension (in-plane translation). Vertical move-
responses of adjacent properties, design ment can also be used to evaluate angular
distortion, which is the differential settlement
Figure 4w: SiltlabciolinzadtCuiocontpoayf dpriaiglrithgyetwnatllanfodlloowrignagndiezmedolistuiornv.ey. divided by the horizontal distance between
two monitored points. Horizontal extension
specification for excavation support using At the conclusion of the pre-construction is important because it is used in conjunction
C inimprovements adjacent to excavation.” survey, a representative from the project with angular distortion to assess potential for
this approach might contain language team and a representative from the firm that structural damage.
conducted the survey should meet with the Captured data from a total station also
and maintain excavation support capable of adjacent property owner or property manager contains out-of-plane translation, which can
to walk them through the survey report and be used to evaluate out-of-plane rotation or
reach agreement with the representations tilt. However, when evaluating movement
contained in the survey report. data, design professionals should consider the
The design professional or specialty engineer impact of environmental factors on building
needs to determine the appropriate time components that are being recorded. The
to require a post-construction survey. The trend plot created from discrete measurements
decision will need to consider anticipated using a total station may show scatter from
durations of construction events. Potential thermal movements that can cloud the trend
times to be considered are when excavation of actual construction-induced movements.
reaches final subgrade, when new construction Use of a tiltmeter or inclinometer instead
reaches grade, or at project completion. results in more meaningful information
Depending on existing conditions of certain to evaluate out-of-plane rotation or tilt.
adjacent structures, the design professional These instruments can be mounted on
eexisting buildings, pavements, and other exterior walls and linked with a data logger
U zbest interests of the adjacent building at the to capture continuous measurements that
resisting soil pressure, hydrostatic pressure, include time and temperature. This type
of monitoring strategy will also capture
and superimposed loads without damaging daily cyclic movements of walls subjected
T R g5), when additional efforts are required to environmental conditions, as well as any
This approach does not necessarily put the
acan become the source of heated debates
forefront of the decision-making process and
S mUnfortunately, this scenario is too often seen in
ato mitigate damage, or when parties have
when: adjacent structures get damaged (Figure

differing opinions on what constitutes damage.

some of the densest urban environments.

Monitoring Building Response may require an interim survey when excavation
reaches final subgrade, and then require a
Monitoring building response during con- final survey at project completion. The pre-
struction is intended to provide information construction survey should form the basis for
on movement and pertinent structural and the post-construction survey. Similar to the pre-
other changes to adjacent structures, as well construction period, a meeting should occur
as information on performance of the construc- with the adjacent owner or property manager.
tion technique. The monitoring program can

be divided into three parts: pre-construction Building-performance Monitoring
and post-construction surveys, building-
performance monitoring, and construction Building-performance monitoring records
diagnostic monitoring. responses of the structure (settlement, transla-
tion, rotation, and vibration) to construction

Pre-construction and activities over a period of time, and frequently construction-induced movements.
Post-construction Surveys enables timely response to mitigate damage. Ground-borne vibrations are best monitored
The design professional or specialty engineer using seismographs with multiple triaxial

A pre-construction survey is used to establishes requirements for the monitoring geophones mounted on the structure. The

document existing conditions of adjacent strategy based on responses of adjacent struc- flexibility of multiple geophones allows

properties prior to the start of any construction tures. Requirements should identify type of a design professional to capture source

activity, including demolition. The survey can instrumentation, specific locations for instru- vibrations at the foundation level, and

include a combination of hand sketches with mentation on adjacent buildings, frequency understand how those source vibrations

narratives, still photographs with annotation of instrumentation recording, method of attenuate or amplify through the structure.

of interior and exterior conditions, and video reporting recorded data, and responsibilities This feature is important because most

(preferably with narratives) of interior and of specific parties for evaluating collected data empirical industry standards are based on

exterior conditions. The survey should be (including mitigation program when pre- vibration levels at the structure base, but

conducted by an experienced individual who established limits are reached or exceeded). occupant discomfort and disruption of

STRUCTURE magazine 18 November 2008

Reporting and Evaluation
nDNeSESOTwOI.EGu3!ENrR1LlaMiDstAeEhsNCetUrKeAE!LFigure 5: Damage resulting from adjacentof Monitoring Data
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construction. A consultant retained to execute the moni-
toring program should prepare summary This edition includes the
T Utenant operations occurs on elevated floors. reports of collected data for distribution to NEW ANSI - SDI specifications.
the design professional, contractor, contractor’s
In addition, measurement of vibration at specialty engineer, and other designees as-
higher levels can be used to evaluate the sociated with the project. The need for
promptness in preparation and distribution
elikelihood of alleged damage. Seismographs of monitoring reports cannot be overem-
phasized. The contract documents should
C incan be set to trigger mode (recording only explicitly state time requirements for distri-
bution, such as within 24 hours of collection
activates when a base magnitude is reached) of data.
Contract documents need to establish
U zor to a continuous mode. Continuous mode
lwaenhcdtiec-hedfpfCmeaocrottpnyybihtraoaisgrsiishrn,etgsapndodantsaei,bvdiallieuttyearttome eiavnpaepluaraoctpearuciaosetle--
provides more information, but also requires
actions to eliminate or slow any movement
amore storage capacity. trends. Without clear ownership, the process
can be ineffective.
Both a data logger for the tiltmeter/incli-
Conclusions
T R gnometer and a seismograph can be connected
Well conceived and executed construction
awith phone or internet service to allow re- monitoring provides vital information re-
garding response of buildings adjacent to
mote access to review and download data or construction, as well as performance due to
construction techniques. Monitoring pro-
S mmodify settings. grams serve as a safeguard against harmful
events. Although development and imple-
mentation of a well-defined monitoring
program may seem expensive at the outset
of the project, lack of one can result in damage
and claims that will likely far exceed program

Although “low tech” compared to other cost. Owners, developers, design profes-
sionals, and contractors need to recognize
instrumentation described, crack gauges the importance of a monitoring program in OTHER HIGHLIGHTS INCLUDE:
are a critical part of a monitoring program. protecting all parties involved in a construc- Detailed Member and Associate Member
These simple devices provide quick tell-tale tion project.▪ contact information
indications of building response to those Completely updated “Code of Standard Practice”

in charge of monitoring building behavior. New ANSI Approved Standards

Typically, crack gauges are installed at Charles Russo, P.E. is a Principal with ANSI/SDI-C1.0 Standard for Composite Steel Floor Deck
existing cracks or at joints between different ANSI/SDI-NC1.0 Standard for Non-Composite Steel Floor Deck
ANSI/SDI-RDC1.0 Standard for Steel Roof Deck

building components where movement can Simpson Gumpertz & Heger Inc., and is Current ASTM material designations
be expected.
Head of Structural Engineering Practice in Information on cellular deck in
Construction Diagnostic Monitoring their Washington, DC office. non-electrified applications
Guidelines for cellular deck floor systems with
Construction diagnostic monitoring systems Michael Brainerd, P.E. is a Senior Principal electrical distribution
record behavior or performance of particular with Simpson Gumpertz & Heger Inc,
construction-related components such as and is their National Practice Leader for ORDER YOUR COPY TODAY AT
underpinning piers and earth support systems. Structural Repair and Rehabilitation.
Diagnostic monitoring information is com- www.sdi.org
pared with anticipated behavior predicted by Milan Vatovec, Ph.D., P.E. is a Principal
analysis to evaluate performance and provide with Simpson Gumpertz & Heger Inc., and
information regarding potential problems. In is Head of Structural Engineering Practice
in their New York office.

addition, monitoring of these components The authors have extensive experience with
provides information that can be used to the investigation of structural performance
understand adjacent building responses. Simi- P.O. Box 25 • Fox River Grove, IL 60021 • (p) 847.458.4647
lar to building-performance monitoring,
construction diagnostic monitoring typically of existing buildings and the rehabilitation This manual is a
has associated threshold and limiting criteria, “must have” for anyone
and uses similar instrumentation (total sta- of structures. You can contact Charles,
Michael or Milan at [email protected], who is responsible
[email protected], or for specifying STEEL DECK.
[email protected].
tion, tiltmeter, and inclinometer).

STRUCTURE magazine 19 November 2008