THEAROTICAL APPROACH AND LITERATURE REVIEW
Numerous tremors hit distinctive urban communities on the planet consistently and lead to expansive harms in the local units, building and frameworks. Many societies lose their lives as a delayed concern of these tremors (and even weighty seizures all over) while thousands lose their homes. The demolition that brought about by the tremor established that even considered quake safe structures were not really safe when seismic removal surpassed the evaluated qualities. Scaffolds situated inside seismic territories are inclined to the loss of solidness and the event of extensive and genuine bends because of weakness in the constituents of the bridge materials.
In this manner, it is important to give security prerequisites to solid scaffolds presented to dynamic loads by achieving a precise and complete investigation of the extension’s capacity to oppose the parallel powers and counteract displeasure in the solid structure of the extension body. Then again,. This section integrates general data about the extensions fit as a fiddle, attributes of the materials associated with developing the body of the scaffold and the powers influencing it.
Likewise, the depiction of essential key of building seismology, fundamental mechanics on seismology and techniques for seismic examination in structures. A few past investigations have likewise been looked into by specialists on solid scaffolds, including exploratory examinations utilizing physical models (shaking table tests) and hypothetical investigations utilizing diverse programming projects (limited component strategy).
2.2 Classification of Bridge Piers
Pier is normally utilized as a general term for a substructure situated between flat ranges and establishments.
Be that as it may, each once in a while, it is furthermore utilized particularly for a strong divider so as to recognize it from segments or bents. From an auxiliary perspective, a section is a part that opposes the parallel power mostly by flexure activity though a pier is a part that opposes the sidelong power fundamentally by a shear system. A pier that comprises diverse portions is every now and again called a bowed. There are a few different ways of characterizing pier types. One is by its auxiliary network to the superstructure: solid or cantilevered. Another is by its sectional shape: strong or empty; round, octagonal, hexagonal, roundabout, curved, chamfered, or rectangular. It can likewise be recognized by its surrounding arrangement: single or various sections twisted; hammerhead or pier wall.
2.3 Materials properties and foundation
Depending on (USBR), the material linked to the structure of the bridges can be ordered into bridge concrete static and bridge concrete dynamic properties.
Static stacking conditions utilized for investigations the solid extension ought to include the impact of drag. Properties of cement vary because of a few parameters, for example, age, evaluating of totals, sort of concrete, and different parts just as their extents in the blend. Since solid blends bit by bit gain quality at different rates, it is important to test the examples of adequate age to allow estimation of extreme qualities. Then again, no information are accessible yet to represent the quality properties under unique stacking.
2- Elastic Properties
The circulation of worry inside solid structures is impacted by a few factors, for example, the Poisson proportion, modulus of flexibility of the solid and the proportion of versatility coefficients for both cement and establishment. In spite of the fact that the modulus of flexibility isn’t straightforwardly corresponding to the quality of the solid, it increments with the quality of cement. For the most part, the versatile modulus of cement is influenced by numerous properties, for example, measure of concrete, evaluating of totals, age and admixtures. The misshaping that happens in a flash with the heap application, for example, amid the seismic tremor, relies upon the dynamic modulus of versatility. The static modulus of versatility and Poisson’s proportion must be determined for the different periods of solid when the chambers are principally stacked. The solid qualities expected to gauge the consequences of the dynamic investigation are the compressive and tensile strengths.
3- Thermal Properties
Amid the development ventures of a concrete bridge pier, warm from cement hydration must be consistently scattered or controlled to keep the presence of unfortunate splitting. Where the warmth created can be diminished by supplanting a measure of the cement with pozzolan, which produces just around 50 percent of the warmth produced by a similar measure of cement. Changes in operational temperature from surrounding air and the waterway can prompt creating serious nonlinear warm inclinations and coupled worries due to of the moderate reaction in the inside of the bridge pier The thermal properties necessary for the estimation of temperature changes are thermal conductivity, diffusivity, specific heat and the coefficient of thermal expansion.
4- Average Properties
Concrete properties can be assessed from distributed information for fundamental investigations until the point when research facility test information is accessible. Along these lines, the accompanying normal measures might be utilized for primer structures until site-explicit test information are accessible. (USBR)
a) Compressive strength-3,000 to 5,000 Ibs/ in2 (20.7 to 34.5 MPa). b) Tensile strength between -5 to 6 percent of the compressive strength. c) Shear strength: Cohesion-about 10 percent of the compressive strength. d) Coefficient of internal friction- l.0. e) Poissons ratio- 0.2. f) Instantaneous modulus of elasticity- 5.0 x 106 lbs/ in2 (34.5 GPa). g) Sustained modulus of elasticity- 3.0 x 106 lbs/in2 (20.7 GPa). i) Coefficient of thermal expansion- 5.0 x 10-6/F (9.0 x l0-6PC). j) Unit weight- 150 Ibs/ft3 (2402.8 kg/ m3).
2.4 Foundation Properties
1- Deformation modulus
The bridge pier examination must include the compelling deformation coefficient and its change on the total contact territory of the pier with the establishment. The deformation modulus can be characterized as the proportion of connected worry to flexible strain in addition to inelastic strain and should be resolved for every establishment material A successful deformation modulus is a composite of deformation moduli for all materials inside a particular piece of the establishment
2- Shear Strength
Amid the plan and development of concrete gravity structures, there are two imperative establishment quality attributes ought to be assessed which are compressive quality and shear quality. Compressive quality is an essential factor in assurance the thickness necessities for a bridge piers at its contact with the establishment. Establishment shake shear quality is given with two factors: attachment (C) and inside contact (?). The qualities for shear quality are commonly decided relying upon the premise of lab coordinate shear test results. Shear quality along the establishment shake/structure interface additionally ought to be performed. Coordinate shear quality lab tests on composite grout/shake tests are prescribed to appraise the establishment shake/structure interface shear quality. The aftereffects of research facility triaxle tests, coordinate shear tests, and in situ shear tests, are for the most part exhibited relying upon the type of the Coulomb condition:
(Shear obstruction) = (unit attachment times territory) + (effective ordinary power times coefficient of inward rubbing) where, R is shear opposition, C is unit union, An is region of the area, N is the compelling typical power, and tan ? is digression of point of friction. Which decides the straight connection between shear resistance and ordinary load.
3- Pore Water Pressure and Permeability
The investigation of a concrete bridge piers establishment requires a data of the hydrostatic weight circulation in the establishment. The permeability is estimated by numerous attributes, for example, the stone sort, the jointing frameworks, the shears and crevices, blame zones, and, at some bridge locales, by arrangement depressions in the stone. The permeability can be constrained by a system of geographical qualities, for example, blames, joints and shear zones. At the point when the establishment grouting and waste or other treatment have been utilized, their consequences for the pore pressures must be included.
4- Compressive and Tensile Strength
One critical factor that is utilized in deciding the bridge piers thickness necessities is the compressive quality of the establishment shake. On the off chance that the establishment shakes is nonhomogeneous; tests must be made for each kind of shake in the stacked bit of the establishment to accomplish compressive quality qualities. The tensile quality of the stone is seldom decided in light of the fact that unhealed joints, shears, and so on, can’t transmit tensile stress inside the establishment.
In the structure procedure of concrete bridges, it is vital to decide the heaps required in the soundness and stress examination. The primary powers which may influence the plan systems are Dead load, Uplift power, Headwater and tail water pressures, Earth and residue pressures, Ice weight, Wave weight, Wind weight, Sub atmospheric weight, Earthquake powers, Temperature and Reaction of establishment. (U.S. Army Corps of Engineers).
1 Dead Load: –
The dead load consists of the weight of the concrete structure of the bridge body.
2 Water pressure:-
Water pressure (P) is the biggest outer power following up on bridge piers. Flat water pressure gotten by the heaviness of water on the upstream and downstream sides of the bridge can be surveyed from the standard of hydrostatic pressure conveyance.
3 Uplift Pressure: –
It is the pressure of the water drainage through the pores and splits in the body of the bridge piers and particularly influences the contact zone between the bridge pier and its establishment.
5 Wave Pressure: –
At the point when the wind blows on the outside of the water in the stream produces waves that create pressure at the highest point of the bridge pier. The pressure produced relies upon the speed of the wind, the profundity of the water in the waterway and the height of the wave.
6 Ice Pressure: –
Load might be impacts on the upstream substance of the extension, as the outside of the water solidifies. On the off chance that the ice gets thick enough, it will cause an extensive load. The heap is focused on a little surface where the extension body is most thinness.
7 Earthquake forces: –
The quake produces waves at various frequencies fit for shaking the ground on which the bridges are situated each conceivable way. In this way, the impact of a seismic tremor is identical to bestowing speeding up to the establishments of the scaffolds in the present heading of the wave. Regularly, a tremor makes even quickening (?h) and vertical increasing speed (?v). The estimations of these increasing speeds are typically communicated as level of the quickening because of gravity (g), i.e., = 0.10 g or 0.20 g, and so on.
1- Effects of Vertical Acceleration (?v)
The impact of a vertical acceleration speed might be either descending or upward. The upward way, the establishment of the extension will be lifted upward and turns out to be closer to the body of the scaffold. In this way, the powerful load of the scaffold will increment just as the pressure created will increment. Then again, when the vertical increasing speed acts descending, the establishment must move downwards far from the body of the extension. In this way, diminishing the successful weight and bridge strength, and consequently is the most pessimistic scenario for plan.
2- Effects of Horizontal Acceleration (?h)
The horizontal acceleration incorporates two parameters:
I) Hydrodynamic Pressure: – Horizontal acceleration towards the upstream prompts a brief increment in water weight, as the establishment and bridge quicken to the upstream and the water opposes the development attributable to its idleness. The measure of this hydrodynamic power (Pe) is communicated as:
Where, Cm is most extreme estimation of weight coefficient for a given consistent incline = 0.735(?/90), where ? is the edge in degree, results from the upstream substance of the bridge with the horizontal bearing; Kh is portion of gravity embraced for horizontal acceleration (?h) = Kh.g.
ii) Horizontal Inertia Force:- notwithstanding utilizing the hydrodynamic weight, the horizontal acceleration makes an idleness drive inside the bridge. This power is created to remain the body and the establishment of the edge together as a solitary piece. The bearing of the created power will be inverse to the acceleration bestowed by the quake. This power is given by:
Where, Kh is the friction of gravity embraced for horizontal acceleration, for example, 0.10 or 0.20, etc.
2.6 Load Combinations
Concrete bridges must be structured mulling over all suitable load blends, by utilizing the best proper safety factor for each. (USBR NO.19))
1 – Usual loading combinations: -Ordinary water height, with legitimate dead loads, residue, ice, elevate and tailwater. In the event that temperature loads are pertinent, least common temperatures will be utilized
2 – Unusual loading combinations: – Most extreme water height, with appropriate dead loads, elevate, tail water, residue and least temperatures happening around then, if applicable.
3 – Extreme loading combinations: – The typical stacking notwithstanding the impacts of the “Most extreme Credible Earthquak “
4 – Other loadings and investigations : -Incorporates: a) The typical or surprising stacking mix just as channels broken, b) dead load and c) the other stacking mix which ought to mull over in the breaking down of a specific bridge.
2.7 Modes of Failure of bridge piers
2.8 Numerical Modelling
Ordinarily, the basic framework is structured fundamentally for gravity loads and not for the horizontal inertial burdens that are produced amid a tremor. The seismic activities on a structure are gotten from bends because of the ground movements brought about by the quake. Thus, they are unique in relation to outside wind or gravity loads, which are connected on the structure.
The utilization of scientific models is a corresponding way to deal with research facility experimentation since they can mimic the dynamic reaction seismic tremors movement. Since expository arrangements are as a rule not accessible for most every day issues in building sciences, numerical demonstrating can assume an essential job in comprehension and anticipating complex crack procedures, giving helpful contribution to break safe plans [R. Das · P. W. Cleary, 2013; Amina Tahar Berrabah,2012].
3.3 Geometry and Design of Bridge Piers
2 -Basic Principal of Engineering Seismology
Seismology is a science who studies earthquakes and seismic waves. Seismic waves are the waves of energy caused by the sudden breaking of rock within the earthquake. When the occurrence of earthquake, there are several different kinds of seismic waves emitted in space surrounding the hypocenter, and they all move in different ways. The two main types of waves are:
Body waves which travel through the Earths interior layers. This type divided into two kinds:
i) Compressional waves which are longitudinal or primary waves (P?waves). P-waves cause alternate push (compression) and dilatation (tension) in the rock as shown in Figure (2-2). Thus, as the waves propagate, the medium expands and contracts, while keeping the same form. They exhibit similar properties to sound waves, show small amplitudes and short periods and can be transmitted in the atmosphere. P?waves are seismic waves with relatively little damage potential.
ii) Shear waves which are transverse or secondary waves (S?waves). S?wave propagation causes vertical and horizontal side?to?side motion. Such waves introduce shear stresses in the rock along their paths as shown in Figure (2-3). Their motion can be separated into horizontal and vertical components, both of which can cause significant damage .
Figure (2-2): Travel path mechanisms of body waves (P- waves)