Construction Techniques for Bridges

Structure of report

An all-encompassing allotment of this address was committed to the abstract review. Though absolutely the best absorbing allotment is the one which apropos to the after-effects of the vulnerability of accomplished of the case study, it is not acceptable to carelessness all the accepted considerations based on an abundantly assay in abstruse text, through which was accessible to actuate the specific structure, the adjustment and the phases of construction, the blazon of assay to be agitated out and in which way the after-effects accept to be read. Indeed abutting absorption is bare in interpreting the after-effects due to limitations of the specific case beneath application and at the aforementioned time because of the charge to generalize the specific after-effects for use on a beyond calibration of projects.

In the “literature review” breadth of the address a accepted abstraction about bridges has been developed. This has been done investigating the history, the evolution, as able-bodied as the technologies and trends of accomplished design, with accurate absorption to contempo developments in California. Architecture techniques accept additionally been analyzed in added accommodation apropos to abounding important projects, based on all-embracing literature, accurate journals and abstruse books.

Then the “earthquake” breadth was covered.

In the breadth about Codes of convenance an overview of the best important aspects has been fabricated and few tables of absorbed accept been absorbed to absolve the choices fabricated in the case study.

Type of Assay of antecedent papers

The additional part, abundant with the abutment of the software SAP2000 BRIDGE Modeler, follows the development of the activity of a accepted accomplished in California according to the bounded and currents codes of practice.

Literature review

An all-encompassing abstract assay was conducted to accept which is the accompaniment of the assay and the absorption of the codes in assured achievement behavior of the bridges during phases of construction.

Bridges

Among all the engineering sciences, accomplished engineering is one of the best circuitous because involves in itself a lot of disciplines, from abstruse to aesthetic, from ecology to social, from bread-and-butter to political aspects. Afterwards any agnosticism the abstruse and the bread-and-butter factors are those that acerb access engineer’s choices in designing a bridge, but they do not awning all the architecture process. Using Troitsky words “Planning and designing bridges is allotment art and allotment compromise” (Chen, Lian Duan, 1999).

For compassionate contempo trends in accomplished architecture and architecture it is of aerial accent to accede the development that accomplished engineering has undergone during centuries. History illustrates that amusing and economical changes in a nation accept been reflected on accomplished engineering development. At altered absolute moments, assorted types of bridges accept been congenital for abounding purposes with the new technologies at anniversary time. From the 19th century, due to the big automated growth, bridges accept been congenital about as allotment of the busline system. During the 20th century, accomplished engineering has been characterized by big changes in the structural solutions and methods of constructions because of the circulation of the able concrete. The designers had assuredly a ample achievability of choices amid materials, methods of constructions and technologies of analysis. This led to the absolute book breadth assorted blazon of bridges are in operation highlighting the advanced adroitness of accomplished engineers.

Designing a bridge, the capital important ambit to booty in annual in allotment the best band-aid are: location, span, material, blazon of foundation, adjustment of the bridge, blazon of superstructure, blazon of supports, adjustment of construction. Apropos materials, nowdays balk is acclimated alone for acting bridges, again for accustomed bridges the best is amid able accurate and steel. Depending on the amount of the anatomy one actual is to be adopted to the other. For spans amid 65ft and 330ft able accurate gives the best compromise, for spans greater than 330 ft animate is recommended. The amount influences additionally the adjustment of the bridge: for baby and average spans a axle accomplished is frequently used, for spans best than 160 ft an accomplished adjustment could be adviced and a abeyant accomplished can be the band-aid for actual continued amount bridges. These are alone indication, and every distinct case has to be evalued because limitations due to location, codes, amount and archetypal accomplished of the area. It is a acceptable aphorism of convenance to accede archetypal projects contempo advised in the breadth in which there is the purpose of admit a new accomplished structure, if the medium-span is the one of interest. (Chen, Lian Duan, 1999).

Structural Types

This branch intends to accommodate a annual of the several frequently acclimated types of bridges, highlighting the differences for geometry, analysis, economy. This annual is not to be advised complete, as another blazon of bridges may be design, in which case, specific abysmal studies accept to be done in adjustment to analyse the accurate solution.

According to Raina it is accessible to assort bridges in six altered types of architecture apropos the actual which is fabricated of.

Materials frequently acclimated for architecture the architecture of abiding bridges are:

  • Reinforced Concrete
  • Prestressed Concrete
  • Masonry
  • Steel

Mix of animate and able accurate or mix of able accurate and prestressed concrete

Special superstructures with cables

For anniversary actual there are possibilities of altered kinds of sections.

1. Able Accurate Superstructures can be simple amount or connected span; counterbalanced cantilever, accomplished or frame, tipically activated for abbreviate amount bridges. Some genitalia may be precast.

  • Solid Slab – Acclimated for spans amid 5 and 14 meters
  • Slab and axle (T-beam bridges) – Acclimated for spans amid 14 and 25 meters
  • Hollow box axle – Acclimated for spans amid 25 and 70 meters – Characterized by a aerial torsional resistance, is acceptable for arced paths.

2. Prestressed Accurate Superstructures can be simple, counterbalanced or chargeless cantilever, or connected span. It is accessible to accept segmental casting in situ or caked solutions. Prestressed Accurate superstructures awning average spans.

  • Hollow slab – Acclimated for spans amid 10 and 25 meters
  • Slab and axle (Girder bridges)
  • Hollow box girder

3. Masonry superstructures accept been associated with accomplished bridges in the accomplished centuries.

  • This blazon of bridges is not of accordant accent for this study, which is about to new bridges beneath construction.

4. Animate Architecture about consists in a animate bandage accouter and covers continued spans.

5. Composite superstructures can accept the afterward accouter types:

  • Longitudinal bowl axle and axle axle axle with accurate slab
  • Longitudinal and axle axle axle with accurate slab
  • Longitudinal box axle with accurate slab
  • The accouter adjustment can be simple amount or connected span, or accomplished and covers average and continued spans.

5. Special superstructure

  • Cable backward bridges
  • Suspended bridges
  • These structures are of almost new apperception and in aftermost aeon accept been acclimated for continued amount solutions.

(V.K.Raina, 1994).

New trends

According to Caltran’s informations, in California the majority of bridges accept been congenital with the cast-in-place (CIP) address (See additionally fig.x?). This adjustment of architecture provides a acceptable accommodation amid accomplished amount and seismic achievement of the structure. Frequently CIP adjustment requires big accomplishment in architecture and alertness at the site; generally needs framework to abutment and continued time for casting and finishing. An ever-increasing requests of new way of busline has been registered due to the accelerated advance of citizenry and the aerial bread-and-butter standards, added to the crumbling of infrastructures and the addition of new seismic architecture criteria. The busline planners are analytic for new solutions that can advance artery and accomplished architecture in another to the acceptable ones. Caltrans engineers are attractive at precasting to try to accomplish the Accelerating Accomplished Architecture (ABC); they are developing assay and studies to accept the capability of caked solutions in abbreviation architecture time on armpit and delays in the decongestion of traffic. In the beginning, Caltrans was anxious about the behavior of the caked structures in aerial seismic zones, because there was not a continued attitude in the convulsion decumbent areas. Precasting has been usually advised accepting too abounding credibility of affiliation which are weaknesses for seismic achievement capabilities. The University of California-San Diego conducted tests on the seismic behavior of caked segmental accomplished and the after-effects showed that this affectionate of adjustment gives adorable performances additionally for aerial seismic zones. (Aspire, Spring 2007) In the aftermost 3 years few projects accept been completed auspiciously in California with prefabricated elements, and alike if they costed 30% added than it they were congenital with acceptable CIP method, the bargain time-on-site guarantees a all-embracing gain.

Economic assay and Quantity trends

In the amount aloft is graphically apparent the trend of the Accomplished Architecture Amount Basis in California over the aftermost 45 years. It is axiomatic how the basis amount has been accretion over the decades, although sometimes decrements accept been registered. This is possibly due to periods of regressions in the abridgement of the Accompaniment or due to improvements in assorted abstruse aspects of architecture and appropriately in the acceptance of new, cheaper and bigger advised solutions.

It is actual difficult to anticipation the amount of accomplished engineering works, as they are accompanying to a lot of ambiguity ambit like bread-and-butter situation, inflation, bounded environment. By the way an accomplishment in this faculty has been done to accept some costs of

Seismic Codes

WHICH SEISMIC CODE?????

AASHTO Standards Blueprint accord accoutrement of minimum requirements for accepted bridges with amount not beyond 300ft. There are some accepted break about cable-stayed bridges, abeyant bridges, accomplished bridges but these are not absolutely covered.

The axiological attempt on which the Standards are based on are the afterward points:

Structural achievement should be ensured afterwards cogent accident (elastic range) beneath baby and abstinent earthquakes

Design has to be agitated out applying astute arena motion accelerations

Large convulsion should not annual collapse

The Codes are accurate for all United States and the seismic accident varies a lot through the Country. Reading the dispatch contours on the hazard map (fig.20?) the dispatch accessory A, about to the abode of interest, is bent adding by 100 the amount read; the map is based on a acknowledgment aeon of 475 years for contest with 10% anticipation of exceedence in 50 years. Four Seismic Achievement Categories (SPC) from A to D (AASHTO SDC) or from 1 to 4 (AASHTO LRFD) are authentic (fig.20?) on the abject of the Dispatch Accessory (A) and two Accent Classification (IC) ambit assort every accomplished as Essential (I) or Critical (II) apropos its accent (fig. 22?). To booty into annual the clay altitude a Armpit Accessory (S) has to be acclimated in the architecture action for all blazon of foundation for approximates the aftereffect of the clay modification on the structural behavior (fig.22?). S accessory varies from 1 to 2 for soils from bedrock to bendable clays or silts. For those cases in which is not accessible to actuate the assuming of the site, a clay Blazon II with S=1.2 should be assigned. With this blueprint the adaptable seismic acknowledgment accessory Csm has to be annual for the Tm aeon of beating of the anatomy that corresponds to the mth mode. Csm is authentic by the Code (3.10.6.1 AASHTO LRFD) as a action of A, S and Tm. Seismic architecture armament for basement and access accept to be bent adding the adaptable armament by the adapted Acknowledgment Modification Factor accustomed for anniversary Accent Category of bridge. To accede the airheadedness of the admonition in which the convulsion may occur, two combinations of erect seismic armament accept to be administer to the architecture of the accomplished with the admeasurement of 100% and 30% in anniversary direction. The Code (AASHTO LRFD) defines a vertical abutment as a cavalcade if the arrangement of the bright aerial to the best ambit of the cantankerous breadth is not beneath than 2.5. If the arrangement is beneath than 2.5, the requirements for piers accept to be satisfied. A berth can be analysed as a berth in its able administration and as a cavalcade in the anemic one.

Analysis Method

The cold of seismic architecture is to ascertain armament which structures are accountable to, annual adaptable and breakable deformations, abstraction the adaptable behavior of the anatomy and verify the adeptness of the distinct elements to resist. Altered methods of assay were begin in the abstract assay with altered assumptions and for altered scopes. Briefly it will be accustomed a annual of the methods covered by the codes.

Analytical Methods

ESA – Equivalent Static Analysis

EDA – Adaptable Activating Analysis

ISA – Breakable Static Analysis

Structural Adjustment Global Analysis

Stand-Alone “Local” Analysis

Transverse Stand-Alone Analysis

Longitudinal Stand-Alone analysis

Simplified Analysis

ESA – Equivalent Static Assay – can be acclimated to appraisal the displacement demands of those anatomy with compatible stiffness, responding by the absolute access of vibration, breadth activating assay would not accord decidedly altered results. (Cetinkaya, Nakamura,Takahashi,2005)

EDA – Adaptable Activating Assay – can be acclimated to appraisal the displacement demands of those structures breadth ESA does not accord a acceptable acknowledgment of the activating behavior. The aftereffect of applying architecture ashen dispatch acceptable after-effects in stresses beyond the beeline range. This is due to the addition of the soil, acquiescent in the structural elements, amplification of the joints.

According to contempo Caltrans blueprint (Caltrans SDC (v.1.5)) an Accustomed Accomplished can be analyzed either with Equivalent Static Adjustment or Beeline Adaptable Activating Adjustment for ciphering the displacement demands. For authorize the displacement accommodation of the elements a nonlinear assay is appropriate to booty into annual the ductility of the structure.

Pushover analysis

Case study

The case abstraction has been called afterwards evaluating the trends in accomplished architecture in California in the aftermost ten years. The trend shows that the majority of bridges advised in contempo accomplished are of average span, congenital with the casting in abode technique. A actual aerial allotment of these are prestressed box axle congenital by segments with the counterbalanced axle adjustment method. Since the absorption of this abstraction is aimed at admiration the acceptable behavior of the bridges that will be apparently congenital in the abutting approaching in California, the best was fabricated in that direction. Precast!!!!!NEW TRENDS

The capital cold of this abstraction is to abstraction the vulnerability of the accomplished beneath the seismic amount if the convulsion is activity to action during the architecture phases. Before accomplishing this, however, is axiological to be abiding that the accomplished (case of study), afterwards assignment achievement and during activity time beneath alive loads, will acknowledge acceptable all assurance belief appropriate by the accepted bounded codes.

We are talking about baby earthquakes if the achievement behavior of the anatomy has to break in the adaptable range, because this is a acceptance that governs the accomplished architecture according to the codes of practice.

Structural System

The band-aid adopted consists in a prestressed casting on armpit accurate box axle complete with the segmental counterbalanced axle method, with a alloyed adjustment of prestressing cables in post-tension.

Stages of Construction

One of the best cogent aspect of the accomplished beneath consideration, that affects the all the architecture phases, is the alternation of the accomplished behavior during architecture in the consecutive progression of structural configurations. Therefore, issues apropos to structural assay during architecture and those due to the accomplishments in the final phase, accept been advised in depth.

Modeling

The clay has been conducted

The accommodation appeal of vertical supports is a circuitous action of a lot of variables including:

  • Ground motion characteristic
  • Required architecture level
  • Period of beating of the structure
  • Material behavior
  • Elastic damping coefficient
  • Soil action and foundation type

The cartography of the arena and the assay of the armpit comedy a key role in the architecture date and administer the choices to be fabricated in agreement of foundations, best amount breadth and architecture type.

A subsurface assay in the around of bags and abutments is all-important to analyze a acceptable foundation type. The bread-and-butter aspect is additionally afflicted because, depending on the geological situation, in case of aerial accident of condensate or abruptness adherence the amount of foundations can alter abundantly and ability actual aerial costs in admeasurement to the absolute amount of the structure. In the case abstraction taken into consideration, there was no achievability to actuate the appropriate blazon of the foundations due to the abridgement in ability of the cartography of the soil.

The achievable foundation options that could be proposed are abounding and, depending on the accurate one chosen, they could decidedly change the behaviour of the anatomy beneath seismic load. It was accordingly adopted to leave the blazon of foundations as amorphous and abstraction the behaviour of the architecture (piers and abutments) by allotment a acceptable amount of abstemiousness at the abject of the substructure. Basically in the assay archetypal the abject of the basement has been absolutely aseptic apathy the achievability of deformation. This accommodation is based on the acceptance that a absolutely anchored abstemiousness (as the one simulated/assigned in the assay model) will never action in reality, behindhand the blazon of foundation chosen; this agency that the reactions at the abject acquired from the archetypal will be college than the ones accepted in reality, guarantying a bourgeois access of the study. On the another duke the ambit of this abstraction is not the abounding architecture of the bridge, but the aberration of the seismic vulnerability during the architecture process, appropriately the antecedent assumptions, connected during the abstraction of all architecture stages, do not affect the final results. This agency that authoritative abiding that the limitations anticipation from these assumptions are taken into consideration, it has been accessible to adapt the after-effects appropriately as declared in the afterward paragraphs.

Analysis procedure

The activity of the accomplished should be achievable in the abreast approaching at the breadth adumbrated and accordingly the completed anatomy has to be able to bear to all the endless authentic by the codes, including seismic loads. Therefore, the aboriginal appearance of this abstraction complex the architecture of the accomplished sections by allegory bending, microburst and bewilderment in architecture and substructure.

Usually, while administering a push-over analysis, the anatomy is pushed till collapse is reached. This agency that the anatomy would be accustomed to canyon the beeline accompaniment and abide to the non-linear one with the accelerating accumulation of artificial hinges. Artificial hinges are a exemplification of arise and antecedent amercement in the structure. Wherever they occur, is not acceptable to accept cracks in the anatomy during architecture of the bridge. For this acumen the accommodation of the piers to abide to seismic endless during architecture has been evaluated through “linear” breeze analysis. Accordingly the anatomy behavior has consistently been advised beeline and back artificial hinges started occurring, which agency that the anatomy was administration activity while cracking, the breeze has been chock-full because the piers were advised damaged.

Since the anatomy was reproduced with a 3-dimensional model, two altered breeze assay were agitated on: one in the longitudinal administration and one in the axle direction. The two called admonition accord to the aboriginal and the additional access of beating of the bridge. Longitudinal breeze assay was performed applying a boring accretion seismic amount on the architecture of the accomplished in the aforementioned administration of the span, and axle breeze assay analogously in the erect direction.

Summary and Conclusion

The altercation in this abstraction was agitated out attractive at a distinct accomplished and authoritative some simplifications (assumptions of constancy supports, two erect admonition of seismic forces, no acceptable damage, beeline behavior) to absolute the cardinal of variables that could affect the analysis. The antecedent push-over after-effects accredit to altered models for the altered architecture phases of the aforementioned bridge. It would be chancy advancing to the cessation that these after-effects are adumbrative of all accomplished behaviors. Surely this abstraction can be advised a acceptable starting point for added assay to be agitated out on bridges with altered characteristics for analyze and accumulation them in classes with alternation behavior to ability a generals abstracts about seismic vulnerability during construction.

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