Probabilistic Fatigue Life Estimation of Steel Bridges by Using a Bilinear S-N Approach
Author: Kihyon Kwon, Dan M. Frangopol and Mohamed Soliman | Size: 1.4 MB | Format:PDF | Quality:Unspecified | Publisher: ASCE | Year: 2012 | pages: 13
This paper focuses on estimating the fatigue life below the constant amplitude fatigue threshold (CAFT) of steel bridges by using a
probabilistic approach on the basis of a bilinear stress life (i.e., the S-N approach). The current AASHTO S-N approach uses a single S-N line
for predicting the fatigue life. However, because of the variation of actual applied live-load stress cycles, this approach very often results in a
severe underestimation of the useful life of structures. It implies that fatigue damage in respective structural steel details may be overestimated.
To improve fatigue life estimation, a bilinear S-N approach is integrated into a probabilistic framework that can model the uncertainties
associated with the fatigue deterioration process. In this approach, the equivalent stress range is computed by using two S-N slopes and
several probability density functions associated with stress ranges. These probabilistic functions are determined on the basis of stress-range
bin histograms from long-term monitoring. An existing bridge that is expected to experience finite fatigue life is used to illustrate the application
of the proposed approach.
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A reliability-based fatigue-damage-evaluation procedure developed
in the companion paper is extended in this paper to incorporate information from
nondestructive inspections (NDI). Since inspections are required at regular intervals,
the results from these inspections can be used for fatigue maintenance of steel
bridges. The sensitivity and capability of some of the inspection methods, including
ultrasonic inspection, are investigated. Inspection information is beneficial; however,
it adds uncertainty to the fatigue-evaluation process. The detectability and
the accuracy are the two additional sources of uncertainty in the NDI. The uncertainties
in them are quantified. The detection events are classified into three cases,
no crack detection, crack detection but without size measurement, and crack detection
with the crack-size measurement. Using the information from k inspections,
the distributions of the basic random variables and the corresponding reliability
index are updated. Using the information on the updated reliability index, a decision
can be made on what to do next, in terms of reducing the next scheduled inspection
interval, or whether to repair, replace, or do nothing. The procedure is explained
with the help of an example. It is concluded that the inspection results can be used
to maintain the fatigue-damage integrity of steel bridges. Fatigue damage-control
curves are also proposed for everyday use
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Author: John W. Fisher, Ben T. Yen, Dayi Wang | Size: 1.27 MB | Format:PDF | Quality:Unspecified | Publisher: ASCE | Year: 1990 | pages: 14
Available experimental data frorm more than 1,200 previous fatigue
tests and some fatigue and fracture tests on full-scale members are compiled and
examined in conjunction with the details and measured live load stresses in riveted
bridges. It is found that the type of riveted detail does not significantly affect
fatigue resistance, that AASHTO fatigue strength category D is a reasonable lower
bound for the initial fatigue crack development, and that the fatigue strength of a
riveted built-up member effectively exceeds the category C resistance curve. It is
also found that the primary members in riveted highway bridges seldom are subjected
to stress ranges that exceed the category D fatigue limit, and thus are not
likely to develop fatigue cracks. The riveted details most likely to develop cracks
are those subjected to distortion or displacement-induced stresses at connections.
Corrosion can reduce the fatigue resistance, but the effect is not critical if the
minimum remaining thickness is not less than one-half of the original thickness.
Recommendations are made for rating riveted highway bridges for fatigue damage.
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Author: E. Bruhwiler, I. F. C. Smith and M. A. Hirt | Size: 1.5 MB | Format:PDF | Quality:Unspecified | Publisher: ASCE | Year: 1990 | pages: 17
Estimates of remaining fatigue life and development of rational maintenance
strategies for riveted bridges are hindered by a lack of knowledge of their
resistance to fatigue and fracture. This paper presents results of fatigue tests of
three types of full-scale riveted bridge girders. If stresses are calculated using netsection
areas, detail category European Convention for Construction Steelwork
(ECCS) 71 American Association of State Highway Traffic Officials [(AASHTO)D]
provides a reasonable estimate of fatigue strength of mildly corroded steel and
wrought-iron elements. Also, the maximum shear stress range in rivets should not
exceed 14 ksi (100 MPa). Fracture properties of wrought iron are examined in
tests of Charpy specimens and fatigue-cracked plates. Fracture toughness of wrought
iron may be low and consequently it is important to obtain data corresponding to
the material employed in the bridge under assessment. If toughness is low, other
factors that contribute to critical crack length (e.g., built-in stresses, geometry,
and loading) become important, since critical crack lengths may not be detectable
under certain conditions. Finally, a two-criteria approach for determination of critical
crack lengths has been identified to be useful for civil engineering structures.
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We lately started taking Reinforced Concrete I and actually I'm finding it difficult focusing with the lecturer so please if any can help me finding a book that can be a startup or even can stay with me along my remaining college years.
Thanks in advance guy's,
Regards,
I forgot to say that we study based on AASHTO - Which is an American Code.
This book examines seven amazing wonders of green technology: BedZED; Earthships, IBM Tower in Kuala Lumpur, Reichstag, the design of the new 7 World Trade Center in New York City, J. M. Tjibaou Cultural Centre Sams in Denmark.
"... In every age, science and technology have advanced human civilization. From architecture to engineering, medicine to transportation, humans have invented extraordinary wonders. People have been constructing buildings for thousands of years. But in modern times, people have become more interested in new kinds of building techniques. They want to make buildings that are "green," or good for the environment. Some green builders make houses out of recycled materials. Others make buildings that use the sun and wind for heating and cooling. In some places, whole communities are based on green building technology. In this book, we'll explore seven wonders of green building technology. We'll learn about Earthships, which collect rain for drinking water and make heat and electricity from the sun's rays. We'll visit Menara Mesiniaga, a skyscraper in Malaysia that is cooled by fresh tropical breezes. We'll explore BedZED, a green community in the United Kingdom that has gardens on rooftops, and we'll visit Samso, an island in Denmark that makes its own electricity from wind turbines. These and other buildings and communities are leading the way to a new, greener future ..."
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Existing design codes recommend hairpins and surface reinforcement
consisting of hooked bars encasing an edge reinforcement
to improve the behavior of anchor connections in shear. Concrete
breakout is assumed to occur before anchor reinforcement takes
effect in the current design methods. This paper presents an alternative
design method for anchor shear reinforcement. The proposed
anchor shear reinforcement consists of a group of closed stirrups
proportioned to resist the code-specified anchor steel capacity in
shear and placed within a distance from the anchor bolt equal to
the front-edge distance. Steel fracture was achieved in the tests of
twenty 25 mm (1 in.) reinforced anchors with a front-edge distance
of 152 mm (6 in.). Meanwhile, the observed anchor capacities
were smaller than the code-specified anchor steel capacity in
shear because concrete cover spalling caused combined bending
and shear action in the anchor bolts. Reinforcing bars are needed
along all concrete surfaces to minimize concrete damage in front
of reinforced anchors for consistent seismic behavior in shear.
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Diagrid tube structures are expected to be used for the outer tubes of super tall tube-in-tube buildings. The mechanical behavior and design method of X-shaped reinforced concrete joints, which are formed by four crossed inclined columns and horizontal girders, are important issues in the design and analysis of vertical crossing lattice tube. Taking the volumetric ratio of the stirrup and the loading pattern as fundamental parameters, four X-shaped reinforced concrete joints were designed and subjected to static axial load testing. The test phenomenon—including deformation of joint zones, development of cracks, and crushing of concrete— is strongly emphasized in the analysis. The laws of the stiffness response and stress development in longitudinal bars and stirrups are revealed, and the ultimate load-bearing capacity of four joints is obtained. The test results show that the stirrups may confine the lateral expanding deformation of the joint concrete regions.
The X-shaped reinforced concrete joints with normal volumetric ratios of stirrups may be designed to provide large stiffness and high load-bearing capacity, which are also effective in transmitting the inner force from four crossed inclined columns. Adopting two loading patterns—agreeing and differential loads—on four inclined columns has little influence on the load-bearing capacity of the joints. Based on the results of the test and analysis, design recommendations and formulas of the bearing capacity for X-shaped reinforced concrete joints in vertical crossing lattice structures are proposed.
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