A comparison of single-run pushover analysis techniques for seismic assessment of bridges

The term ‘pushover analysis’ describes a modern variation of the classical ‘collapse analysis’
method, as fittingly described by Kunnath [1]. It refers to an analysis procedure whereby an
incremental-iterative solution of the static equilibrium equations has been carried out to obtain
the response of a structure subjected to monotonically increasing lateral load patterns. Whilst the
application of pushover methods in the assessment of building frames has been extensively verified
in the recent past, nonlinear static analysis of bridge structures has been the subject of only limited
scrutiny [2]. Since bridges are markedly different structural typologies with respect to buildings,
observations and conclusions drawn from studies on the latter cannot really be extrapolated to the
case of the former, as shown by Fischinger et al. [3], who highlighted the doubtful validity of
systematic application of standard pushover procedures to bridge structures.
Recent years have also witnessed the development and introduction of an alternative type of
nonlinear static analysis [4–10], which involve running multiple pushover analyses separately, each
of which corresponding to a given modal distribution, and then estimating the structural response
by combining the action effects derived from each of the modal responses (i.e. each displacement–
force pair derived from such procedures does not actually correspond to an equilibrated structural
stress state). As highlighted by some of their respective authors, the main advantage of this
category of static analysis procedures is that they may be applied using standard readily available
commercial software packages, since they make use of conventional analysis types. The associated
drawback, however, is that the methods are inevitably more complex than running a single pushover
analysis, as noted by Maison [11], for which reason they do not constitute the scope of the current
work, where focus is instead placed on single-run pushover analysis procedures, the simplicity
of which renders them an even more appealing alternative, or complement, to nonlinear dynamic
analysis [12].
In this work an analytical parametric study is thus conducted applying different single-run
pushover procedures, either adaptive or conventional, on a number of regular and irregular continuous
deck bridges subjected to an ensemble of ground motions. The effectiveness of each
methodology in reproducing both global behaviour and local phenomena is assessed by comparing
static analysis results with the outcomes of nonlinear time-history runs. Adaptive pushovers are
run in both their force-based [13–17] and displacement-based [18, 19] versions. With respect to
the latter, it is noted that, contrary to what happens in a non-adaptive pushover, where the application
of a constant displacement profile would force a predetermined and possibly inappropriate
response mode that could conceal important structural characteristics and concentrated inelastic
mechanisms at a given location, within an adaptive framework a displacement-based pushover
is entirely feasible, since the loading vector is updated at each step of the analysis according to
the current dynamic characteristics of the structure. The interested reader is referred to some of
the aforementioned publications for details on the underlying formulations of adaptive pushover
algorithms.
It is observed that whilst for regular bridge configurations some conventional single-run pushover
methods may manage to provide levels of accuracy that are similar to those yielded by their more
evolved adaptive counterparts, when irregular bridges are considered the advantages of using the
latter become evident. In particular, the displacement-based adaptive pushover (DAP) algorithm is
shown to lead to improved predictions, which match more closely results from nonlinear dynamic
analysis.
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Technical Guidance for Bridges over Waterways with Unknown Foundations

The term “unknown foundations” has been traditionally associated with examining the population of existing bridges over waterways (riverine and tidal) where foundation details are unknown and therefore, foundations could not be evaluated against the hydraulic hazards related to scour. Most of the bridges having unknown foundations were identified by owners while screening their bridges over waterways (riverine and tidal) for their scour vulnerability. These bridges received a Code U for Item 113 of the FHWA’s Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges (Coding Guide).
The FHWA exempted this population of bridges from being evaluated for their scour vulnerability due to the lack of a process and guidance that would have allowed bridge owners to determine their foundation characteristics and therefore, evaluate these bridges. This exemption did not apply to bridges on Interstate designated routes for which FHWA recommended bridge owners to consider technology available to determine their foundation characteristics and evaluate their scour vulnerability. The use of geophysics technology such as non-destructive testing (NDT) has been available for quite some time; however, cost and reliability of results may be the leading reason for their limited use for determining foundation characteristics.
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National Bridge Inspection Standards – Scour Evaluation and Plans of Action for Scour Critical Bridges

The purpose of this memorandum is to request your assistance towards ensuring that Federal Agencies (referenced herein as bridge owners) complete the scour evaluation of their bridges over waterways (riverine and tidal). Also, we request your assistance towards ensuring that bridge owners develop and implement a Plan of Action (POA) for each bridge identified as scour critical to meet the requirement set forth in the National Bridge Inspection Standards (NBIS) regulation
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Status of Bridge Scour Evaluations and POAs for Scour Critical Bridges

Bridge owners have been working for several years towards the evaluation of their bridges over waterways to determine foundation vulnerability against stream instability and scour. To date, about 93 percent of these bridges have been evaluated. We must, however, make sure that all bridges over waterways are evaluated for their vulnerability to stream instability and scour. As of August 2007, bridge owners reported on their National Bridge Inventory (NBI) data submission a total of 34,900 bridges over waterways that still remain to be evaluated as for their scour vulnerability. These are bridges that have been coded 6, T, or Null for Item 113 of the NBI. The FHWA established a target date of January 1997 for completing all scour evaluations by memorandum dated July 15, 1991; however, as the NBI data shows, we still have work to do to complete this important component of the NBIS. Table 1 presents the number of bridges over waterways on the National Highway System (NHS) and the non-NHS that still need a scour evaluation. Another 67,039 bridges over waterways identified by bridge owners as having unknown foundations remain to be evaluated for their scour vulnerability as of August 2007. We will address the subject of unknown foundations, including a process developed by the FHWA’s Office of Bridge Technology to identify bridge foundations characteristics under a separate memorandum
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Perencanaan dan pelaksanaan konstruksi jembatan gantung untuk pejalan kaki

Pedoman tentang Perencanaan dan pelaksanaan teknik jembatan gantung untuk pejalan kaki adalah revisi dari SNI 03-3428-1994, Tata cara perencanaan teknik jembatan gantung untuk pejalan kaki dan SNI 03-3429-1994, Tata cara pelaksanaan jembatan gantung untuk pejalan kaki, dengan melakukan modifikasi terhadap pengguna jembatan, kelas jembatan, besarnya beban hidup, syarat bahan, dan dilengkapi dengan contoh perhitungan manual yang diklarifikasi dengan hitungan program elemen hingga.
Pedoman ini disusun oleh Panitia Teknis Bahan Konstruksi Bangunan dan Rekayasa Sipil melalui Gugus Kerja Jembatan dan Bangunan Pelengkap Jalan pada Subpanitia Teknis Rekayasa Jalan dan Jembatan.
Tata cara penulisan disusun mengikuti Pedoman Standardisasi Nasional (PSN) Nomor 8 Tahun 2007 dan dibahas pada forum konsensus tanggal 19 Desember 2007 di Bandung, yang melibatkan para nara sumber, pakar dan lembaga terkait.
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Acomparison of single run pushover analysis techniques for seismic assessment of bridges

Traditional pushover analysisis performed subjecting the
structure to monotonically increasing lateral
forces with in variant distribution until a target
displacement is reached both the force distribution and
target displacement are hence based on the assumption
that the response is controlled by a fundamental
mode,that remains unchanged throughout.
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Bridge Construction Details

THERE is a wide variation in the complexity of bridge
construction details that satisfactorily perform identical
functions. These details have a profound effect on the cost of
short span bridges and should be afforded more attention than
is usually given to them.
One study has shown a range in cost from $0.22/lb to
$0.16/lb for the same structure with different framing and
details. This has more significance than the 38 percent spread
in these prices. Assuming the material cost to be $0.08/lb and
deducting this cost from the total, the amount required for
fabrication and erection (the remaining portion of the cost) is
$0.08/lb for one and $0.14/lb for the other. This is a 75
percent variation in the cost of fabrication and erection due to
differences in the design of the framing and details.
To achieve the minimum cost, bridge details should be
examined in the light of their intended functions. The least
sophisticated device that will satisfy the need will generally
be the least costly. For all details used in the construction of
bridges, the AASHO and AREA specifications provide a
latitude of choice, with restrictions imposed by individual
states or railroads due to geographical differences and special
preferences. However, it is not uncommon to disregard this
latitude of choice and select standard details, instead of
applying objective consideration to the specific need for the
detail. This can be costly.
AISC has studied a large number of details contained in
the standards submitted by 32 state highway departments. A
selection was made of typical details which
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Wind Loads for 19th Century Bridges:Design Evolution, Historic Failures,and Modern Preservation 2007

Preservation of 19th century truss bridges can be accomplished by
rehabilitation into pedestrian bridges.But most vehicular truss
bridges from the 19th and early 20th centuries were designed for
much lower wind pressure than mandated today.Engineers trying
to rehabilitate such bridges often find insufficient lateral resis-
tance in the historic structures.Engineers involved with suchre-
habilitation projects follow the Guide Specifications for Design of
Pedestrian Bridges (AASHTO1997),which basically mandatesa
wind pressure of 3.59 kPa (75psf).How did his requirement
originate?This paper will explore 19 th and early 20 th century
event significant to the development of standards for design wind
pressure.
The success of the patent truss bridge in the 19 th century had
its roots in the westwardex pansion of the United States,which
created a demand for bridges of increasing span and capacity in
ever-increasing numbers.The principal advantages of trusses,
whether they are timber,iron,or steel,are economy and speedof
construction.However,these advantages are not attained without
trade-offs:light weight trusses were—andare—susceptible to
wind.
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