CONCEPTUAL ANALYSIS BASED ON CARBON FIBER REINFORCED POLYMERS Prakash Narayan
Research Scholar, Department of Civil Engineering, RGPM College, Bhopal (M.P.) Mr. Rajesh Joshi
Professor, Department of Civil Engineering, RGPM, Bhopal
Abstract - Vehicle collisions with piers can cause serious column damage and catastrophic damage to the entire structure. The country's sick infrastructure shows that many structures no longer meet current construction standards, and that many bridges are prone to failure during the extreme load event. The purpose of this study is to investigate the structural response of reinforced concrete columns to vehicle collisions. Sensitivity analysis is performed to investigate the causes of pier shear and bending rupture in vehicle collisions. In this study, we will look at parameters such as column diameter, side reinforcement spacing, vehicle impact speed, pile head height, and multiple column configurations. The finite element code LSDYNA is used to simulate and analyze vehicle collisions for accurate and detailed results. These studies include the National Crash Analysis Center and the National Transportation Research Center, Inc. The vehicle model is used. The control and material properties of finite element modeling are verified by hammer experiments. The pier collision model is validated by comparing vehicle damage and impact forces with published studies. Energy savings are also checked to ensure stability within the impact simulation.
Sensitivity analysis suggests that various support parameters have a significant effect on failure type and impact force distribution. Rigid columns provide high impact forces, low lateral displacements, and high resistance to lateral forces and bending moments. Performance-based analysis shows that columns can be designed with damage rates associated with a particular damage condition.
1. INTRODUCTION
Around 3 am on May 22, 2011, a semi- trailer truck carrying newspapers and magazines collided with an elevated SC Highway 150 north of I85 near Gaffney, South Carolina (Kudelka2011). The impact force of the destroyed the collision of the columns and half of the curved canopy, damaging the other two columns and sagging the span of the superstructure. Figure 1.2 shows the damage caused by a collision. 52 hours after the accident, traffic north of I85 resumed after the damaged part of the viaduct was demolished. After that, the entire overpass was replaced with a completely new bridge, which took four months to build. On October 21, 2011, the SC Highway 150 Lane was reopened.
Figure 1.1 Damage caused by the tractor-trailer collision with the SC Highway 150 bridge over I-85 (Smoke
2012)
On June 11, 2012, a semi-trailer truck equipped with various electronic devices ran westward around 4 pm at I30 in Dallas, Texas. The driver is said to have fallen asleep on the wheels and collided with a stanchion on the Dolphin Road Flyover Bridge (Vega2012). Due to the high impact, the tractor cab and part of the trailer were split in half. The impact shown in Figure 1.3 caused shear failure in the easternmost column, requiring urgent repairs to stabilize the viaduct.
The highway was closed for more than 15 hours and it took about a week to repair the bridge.
1.1 Objectives/Scope of Research The purpose of this study is to: (1) Perform a thorough literature review to understand the interactions and processes associated with collisions with vehicle columns, and how to investigate such events using finite element modeling. (2) Model the collision event to ensure that the material model and finite element process are working properly. (3) We will verify the accuracy of the vehicle model by modeling a single pillar and comparing the analysis results with the
published results. (4) Perform sensitivity analysis to observe the effects of pier diameter, tire clearance, vehicle impact speed, pile head height, and pier deflection on pier structural resistance and response.
2 LITERATURE REVIEW
The American Society of Civil Engineers (ASCE) has released a report outlining the state and performance of the country's construction infrastructure. The evaluation of the report is similar to the school report, where A indicates an exceptional condition and F indicates a failure. The condition of the National Bridge received a mediocre rating of C +.
As of 2013, there were 607,380 bridges in the United States. Of these, 66,749 are structurally defective and 84,748 are functionally outdated (ASCE2013).
Structurally defective bridges require significant maintenance, refurbishment, or complete replacement. Functionally obsolete bridges are obsolete and do not meet today's building codes. This suggests that nearly 25% of national bridges do not meet design criteria and are prone to failure when exposed to extreme stress events. The median age of all bridges in the United States is 42 years. Approximately $ 12.8 billion is spent annually on improving national bridges, but an additional $ 8 billion is needed to reduce the unprocessed labor required to keep all bridges at the right level. It is estimated that this will happen.
Harik et al. (1990) Reported the causes of bridge failures in the United States from 1951 to 1988. The 114 failures were divided into two categories:
complete collapse and partial collapse.
The complete collapse consisted of columns, spans, or bridges that could not withstand the design load due to the loss of most substructures and superstructures. The partial collapse consisted of a bridge that required only a partial closure of the bridge. The causes of the observed bridge failures were vehicle accidents, building types and ages, and obesity. Most of the vehicle collisions observed occurred on trucks, ships and trains.
Wardhana and Hadipriono (2003), Harik et al. repeated the same investigation as. (1990) several years from 1989 to 2000. Causes of bridge failures
during this period included hydropower, collisions, overloads, damage, fires and earthquakes. Of the total of 503 of the bridge failures analyzed during this period, 59 of were the result of vehicle collisions 14 from cars and trucks, 10 from barges, ships and tankers, 3 from trains, 32 from other sources of collision.
Vehicle collisions are the third leading cause of bridge breakdowns, accounting for almost 12% of all bridge breakdowns after floods and scours.
3 VEHICLE IMPACT FORCE
Vehicle collisions with piers are a complex interaction. To ensure the stability of the bridge structure, the force generated by the impact must be absorbed and absorbed by the stanchions and the impact vehicle. Impact energy is dissipated by heat, sound, and deformation from the pillars of vehicles and bridges. The next chapter describes how the impact force of a vehicle is determined and derived during a collision event.
3.1. Stages of Vehicle Collision
Collision events that occur between a moving vehicle and a stationary pier can be divided into two phases. The first stage occurs until the vehicle and pier have a common speed and move together during the first contact time between the vehicle (including the initial speed) and the pier.
The vehicle will wrinkle and begin to absorb some of its kinetic energy. The resulting force is relatively small. When the vehicle reaches a point where it can no longer absorb energy, the remaining kinetic energy is transferred to the pillars of the bridge. When enough energy is transferred to the pillar, the speed of the vehicle will match the speed of the pillar and will start moving accordingly. This is when the second stage begins. The second stage occurs between the time the vehicle and the pier start moving together and the time the pier breaks down or the vehicle stops. The force generated in this phase is much greater than the force generated in the first phase. Breakage of bridge girders most often causes shear breakage at or around the impact point.
This shear failure is a direct result of cracks and cracks in the concrete surface across the cross section of the column.
The force transmitted to the pillars in the
event of a vehicle collision is identified as the necessary force the pillars must withstand. This force is highly variable and depends on the stiffness, mass, velocity of the colliding vehicle and the structural and material properties of the pier. (Sharma et al. 2011)
4 VALIDATION OF FINITE ELEMENT MODELS
An important part of using finite element analysis in your research is to make sure that your model represents exactly what the model represents. Physical properties such as shape, material properties, and boundary conditions must exactly match the experimental setup. The model can be verified by comparing the displacement and force with the experimental results.
Since the experimental data of the vehicle collision with the pier was very limited, the experiment using the same impact phenomenon was used for the verification. In the current study, a series of tests by Fujikake et al. (2009) was used to verify finite element control and material properties for use in vehicle collision simulation. The test consisted of 4,444 reinforced concrete beams that had been subjected to a drop hammer test.
Hammers fell at various heights, intermediate deflections and impact forces were recorded and used for verification.
The following finite element model was created in N, mm, seconds.
4.1. Beam Impact Experiment Setup Impact loads were applied to a series of reinforced concrete girders 250 mm deep, 150 mm wide and 1,700 mm long (Fujikake et al. 2009). Figure 4.1 shows the placement of the reinforcing cage and the dimensions of the test beam. Around the reinforcement cage was a 40 mm concrete cover, except for the edges that covered 25 mm. The concrete girder was reinforced with four vertical rebars (two for compression and two for tension) and 23 horizontal rebars at a distance of 75 mm. Three beam types are modeled, each with a different ratio of vertical rebar to total beam cross-sectional area ρ. The first beam S1616 consisted of a D16 bar with ρ 2.12% compressed and decompressed. The second bar, S1322, consisted of a compressed D13 bar and a drawn D22 bar, with a ρ of 2.40%. The third beam S2222 consisted of
compressed and stretched D22 bars with a ρ of 4.13%. All lateral rebars consisted of D10 rebars with yield strength of 295 MPa. The yield strengths of the vertical bars D13, D16, and D22 were 397, 426, and 418 MPa, respectively. According to the concrete standard of the Japan Society of Civil Engineers (JSCE) (Fujikake et al. 2009), the estimated bending strength was lower than the shear strength, so three reinforced concrete beams were used as bending control beams. The concrete compressive strength at the time of the test was 42.0 MPa. Table 01 shows the mix ratio of ready-mixed concrete for reinforced concrete beam samples. The maximum grain size of concrete was 10 mm. The girder span was 1,400 mm and was supported by two specially developed supports. This allowed the carrier to rotate freely, but the carrier did not move vertically and vertically. Figure 4.2 shows the drop hammer test setup.
Figure 4.1 Schematic illustration of the beam cross-section (top) and side view
(bottom)
5 FINITE ELEMENT MODELING OF VEHICLE COLLISIONS WITH BRIDGE PIERS
The next section outlines the process and results of finite element modeling of vehicle collisions using pillar simulation.
These simulations are an efficient and inexpensive way to study vehicle-column collisions. This is because many simulations can be run to fully understand all the mechanisms involved in collision events. Three vehicle models were investigated and validated for use in modeling vehicle collisions with columns.
The vehicle collision simulation was
validated by comparing the results with published reports using a similar simulation.
5.1. Vehicle Models
Three vehicle models were used to simulate a vehicle collision with a pier.
The three vehicles selected are the Chevrolet C2500 pickup, the Ford F800 single unit truck, and the semi-trailer.
The reduced C2500 model shown in Figure 5.1 has a total element count of 10,518 and a total mass of 1.84 Mg. The F800 model shown in Figure 5.2 has a total element count of 35,353 and a total mass of 8.06 Mg. In 5.3, there were a total of 355,068 elements and a total mass of 13.15 Mg. These vehicles were chosen to represent small, medium and large trucks. The vehicle model was used "as is". NS. It hasn't changed anyway. In addition to setting the initial velocities of various impact velocities. The kinetic energy of the moving vehicle shown in Figure 5.4 was calculated according to Equation 01 for collision velocities 55, 90, 110, and 135 km / h.
Figure 5.1 Finite element model of a Chevrolet C2500 pickup truck
Figure 5.2 Finite element model of a Ford F800 single-unit truck
Figure 5.3 Finite element model of a tractor-trailer truck
Figure 5.4 Kinetic energy versus impact velocity for the vehicle models 5.2. Vehicle Collision Validation
To verify the accuracy of the finite element model, you need to verify the simulation response using the results of the experimental tests available. Vehicle models C2500 and F800 have been validated using the method developed by El Tawil et al. (2005), Mohammed (2011) and Agrawal et al. (2013). The tractor trailer model was validated using the method developed by Buth et al. (2011).
Another important aspect of ensuring that the finite element model is working properly is to monitor and minimize the amount of energy in the hourglass installed in the system to an acceptable amount.
6 SENSITIVITY ANALYSIS OF PIER PARAMETERS
Sensitivity analysis was performed to evaluate the effects of various parameters such as column diameter, tire lateral clearance, and vehicle impact speed. Two studies were conducted to observe the effect of pile head height and to model the pier as part of a curved configuration consisting of multiple columns. This section outlines the AASHTO LRFD specification for pier design, the process
of developing a vehicle collision model for LSDYNA analysis, and the impact of the results. The purpose of this study was to observe the various types of failures that can occur when a pier is exposed to a vehicle collision. Therefore, not all supports in the following parametric studies have sufficient shear strength against the impact load of the vehicle.
6.1. Aashto LRFD Bridge Pier Design Specifications
A complete review of AASHTO's design specifications has resulted in the production of 4,444 columns with realistic values for material properties, dimensions and strength capacity. The following decisions were taken into account and used to build the pillars of this parametric study.
6.1.1. Material Unit Weights
The unit weights of various building materials were given as follows: 22.78 kN /m3 (2,325 kg/m3) for normal concrete with a compressive strength of 35 MPa or less, 76.98 kN/m3 for steel parts: (7,850 kg/m3), 18, 85 kN/m3 (1,922 kg / m3) for compressed sand, silt, or clay, 15.71 kN/m3 (1,602 kg) for loose sand, silt, or clay /m3). (AASHTO, 2012). The minimum concrete strength for bridge parts is 16.5MPa.
6.1.2. Concrete
Five concrete classes are defined for different types of concrete used in different structural elements and are shown in Table 5.4. (AASHTO 2012).
Concrete class A was selected as the main concrete class for the following parametric studies. The material properties of Class A concrete are minimum cement content 362kg /m3, maximum water cement ratio 0.49, coarse grain size 4.7525 mm, compressive strength 28 MPa for 28 days (AASHTO2012). The modulus of elasticity Ec was calculated using the following equation:
Equation 6.1 K1 is assumed to have an aggregate source correction factor of 1.0, wc is assumed to be units of concrete (Mg/
mm3), and f`c is the specified compressive strength (MPa) of concrete. The elastic
modulus of the concrete used was 25.35 GPa. The Poisson number is assumed to be 0.2. Fatigue potential used the following formula
Equation 6.2 Where fc s in MPa. The modulus of rupture for the concrete was calculated to be 3.34 MPa.
Table 5.12 of the AASHTO LRFD outlines the various cover depths specified for unprotected rebar (AASHTO2012). The main bar protected by the epoxy coating should have a cover depth of at least 25 mm. Since the piers to be modeled were assumed to be exposed to de-icing salt, a 65 mm concrete cover depth is required to protect the rebar cage from corrosion (AASHTO2012).
6.1.3. Reinforcing Steel
The bar used for reinforcement must have a nominal yield strength of 420 520 MPa.
A nominal yield strength of 420 MPa was selected to improve the parameter study.
The modulus of elasticity was assumed to be 200 GPa. At least 6 vertical bars No. 16 should be placed in a circle on the round reinforced concrete columns. The area of the vertical rebar should be 0.010.04 times the total cross-sectional area of the column, according to section 5.10.11.4.1a (AASHTO, 2012). The size of the horizontal rebar depends on the size selected for the vertical rebar. No. 32 No.
32 when using 32 or less bars for vertical reinforcement. Use 10 bars for 10 side reinforcement. Otherwise, bar number 13 is used for lateral reinforcement. The maximum distance between the lateral reinforcements of the compression rod should not exceed the column diameter of or 300 mm, as specified in Section 5.10.6 (AASHTO 2012).
6.2. Bridge Pier Models
The model developed for this sensitivity analysis consists of three main components: columns, foundations and vehicles. An exemplary layout view of the entire model is shown in Figure 6.1.
AASHTO's design specifications were used to design the pillars of sensitivity analysis research. The pier consisted of round reinforced concrete columns 5 meters
above the surface. Above the pillar is the mass of a 250 ton cylinder with a height of 1 m. It represents the mass of the superstructure, which is proportional to the area of the tributaries supported by the columns. In this parametric study, we examined three column diameters of 600, 900, and 1,200 mm. The columns were reinforced with 6, 12, or 24 vertical bars No. 25, achieving a vertical reinforcement rate of 1%. The columns were laterally reinforced with ring bar No. 10 at intervals of 50, 150, and 300 mm to determine the effect of lateral reinforcement on the column shear strength. The bracket spacing considered corresponded to AASHTO's requirements for concrete compression bars. A 65mm concrete cover was planned for all pillars.
Figure 6.2 shows a design example of the pier cross section. The compressive strength of concrete is 28 MPa, the maximum particle size is 24 mm, and the mass density is 2,325 k /m3. It was assumed that the yield strength of the reinforcement was 420 MPa, the elastic modulus was 200 GPa, the tangential coefficient was 1,500 MPa, and the mass density was 7,850 kg / m3. The effect of velocity on the yield point of the rebar was modeled using the dynamic gain coefficient equation by Malvar and Crawford (1998). The support was carried by a deep tubular pile foundation. This will be discussed in more detail later in this chapter. The yield strength of the tubular pile is 250 MPa, the elastic modulus is 200 GPa, the tangential coefficient is 1,500 MPa, and the mass density is 7,850 kg / m3. A layer of elastic material with a thickness of 50 mm was applied to the pile head. This corresponds to the weight of a layer of soil at a depth of 1m supported by the foundation.
Vehicle collision speeds are set at 55, 80 and 120 km / h.
Figure 6.1 Complete model for vehicle collision with a bridge pier
Figure 6.2 Cross sectional layout of 900 mm diameter bridge pier 6.2.1. Deep Pile Foundation
The soil that supports the pillars is extremely dense sand with a unit weight of 21.0 kN/m3 (21.43 kg/m3), an internal friction angle of 40°, and an allowable earth pressure of 250 kPa. Deep pile foundations were used to support the columns. The foundation consisted of 4,444 pile heads with nine PP360 x 11.12 tubular piles. The tip of the pile head is placed 1 m below the assumed terrain surface. The pile head is designed as a square mat foundation according to the ACI specification (Coduto 2001). The pile head of the pier with a diameter of 600 mm and 900 mm is 3.5 m wide, 3.5 m long and 1 m deep. The 1200mm diameter peer cap is 3.6m wide, 3.6m long and 1m deep. The pile cap is reinforced with 9 rods No. 13 on the X and Y axes. The matting and reinforcement of the pile head element is shown in Figure 6.3. Fixed connections on the underside of tubular piles were considered.
Figure 6.3 Mesh used to connect pier to pile cap with pile cap reinforcement
shown
Pile Use the American Petroleum Association (API) method to determine the load-displacement curve of laterally loaded sand to effectively capture the interaction between the foundation and the surrounding soil. Did API, 2005). The load-displacement curve shows the stiffness of the surrounding soil at various depths along the length of the pile and was modeled on inelastic springs.
Springes were installed every 500 mm (along the horizontal plane) along the length of the X-axis and Y-axis piles.
Since the floor has no tensile stiffness, the springs are tuned to act only on pressure.
The spring was created from discrete elements 250 mm long and in length, and the stiffness characteristics were modeled on LSDYNA's inelastic spring model. All springs of the same depth are assigned the same material and cross-sectional properties. For the dense sand surrounding the foundation, an effective soil weight of 21 kN / m3 and an internal friction angle of 40° were assumed. The pipe pile had a diameter of 360 mm and a length of 6000 mm. At a given depth, the final lateral bearing capacity of the sand was determined from Equation 03 for shallow depths and from Equation 04 for deep depths as a minimum.
Equation 6.3
Equation 6.4 Where pu, is the ultimate lateral bearing capacity (kN/m) (S = shallow, D =
deep), Y is the effective soil weight (kN/m3), H is the soil spring (m), the C1, C2 and C3 coefficients are determined from Figure 6.8.6-1 of API (2005) as a function of the internal friction angle, and the average pile diameter, D from surface to depth (m), and were defined as 4.6, 4.25, and 100, respectively. For each soil spring spaced at 500 mm along the length of the piles, a p - y curve was defined describing the lateral soil resistance at each depth versus the lateral displacement of the foundation.
These p – y curves for sand are nonlinear and were approximated using Equation 0- 5:
Equation 6.5 Where A is the factor to account for cyclic or static loading condition, pu is the ultimate bearing capacity at depth H (kN/m), and k is the initial modulus of subgrade reaction (kN/m3). Determined as a function of angle of internal friction, using Figure 6.8.7-1 of API (2005), y is the lateral deflection (m), and H is the soil spring depth (m).
Equation 0-5 was used to determine the resistive force per length of foundation to laterally displace the pile.
The curves were multiplied by the tributary length of the springs, 500 mm, to give the spring stiffness p − ycurves for various depths, shown in Figure 6.4.
Figure 6.4 Example of the spring stiffness p-y curves used for the soil
springs
6.2.2. Stress Initialization through Dynamic Relaxation
Piers carry enormous loads due to the mass imposed by the sturdy superstructure they support. Piers exposed to gravity do not have the same compressive strength as unloaded piers.
Therefore, before running a vehicle impact simulation, it is necessary to develop a model of the pier under gravity. When the column is subjected to an axial load, the Poisson`s ratio causes the concrete material to expand slightly laterally. The tensile strength of the rebar helps to control and reduce the expansion of the concrete core and slightly increases the compressive strength of the concrete. This limiting effect plays a major role in the response of the structure to impact loads.
Side reinforcement of the compression bar helps to provide shear strength, but also helps to surround the concrete core under axial loads.
LSDYNA uses three methods to create the first loaded equilibrium state.
Quasi-static transient analysis with mass decay, explicit dynamic relaxation, and implicit dynamic relaxation. Dynamic relaxation is an analysis used to precharge the system before starting the normal transient analysis phase. Preload and displacement are usually very small.
Dynamic relaxation effectively damps the system and reduces the calculated node velocity until the distorted kinetic energy is reduced to the convergence limit. When the convergence limit or end time is reached, the dynamic relaxation phase ends and the transient analysis phase begins.
LSDYNA stress initialization methods, gravity increases slowly over time. This prevents the dynamic vibration of the elements that can occur with short accelerations. Voltage initialization based on quasi-static transient analysis with mass attenuation involves the application of gravity curves. The gravity curve rises and remains stable during normal transient analysis. Then apply mass damping to reduce the dynamic vibration of the element until preloading occurs.
Once the preload conditions are established, the mass drop is reduced to zero. As soon as the precharge state is reached, the rest of the analysis will continue. Although this method is easy to use and implement, it is excluded from
vehicle impact surveys because it cannot be used for problems using initial velocity.
6.2.3. Vehicle Model
The impact vehicle used in this parametric study was the 1997 Ford F800 Single Unit Truck (SUT) model. The F800 truck weighs 8,063.4 kg and is classified as a Class 5 truck with a total vehicle weight of 7,2588,845 kg. Represents a medium-duty truck. We investigated the collision speed of trucks at 55, 80 and 120 km / h. Vehicles with bumpers were placed about 120mm from the pier. The engine compartment of the F800 SUT collides with a pier at a height of 0.51.7m above the ground. The only change to the F800 SUT was the initial speed. It should be noted that the vehicle model used in this study had about one-third of the vehicle weight used to determine the vehicle collision force of 2,669 kN specified in the design rules. There is.
6.2.4. Model Input Parameters for Transient Analysis
The following input parameters were used in the vehicle impact analysis: At this stage of the modeling process, we started dynamic relaxation and no longer needed the map used to collect the data for motion initialization.
Various parameters were used to control the transient analysis. The energy of the hourglass is calculated and included in the energy balance. This will take the hourglass into account and record it in the impact analysis. The Flanagan Bellychko Rigid Hourglass Control was used to control the hourglass in the system. An hourglass factor of 0.05 was taken into account. Using the automatic ground contact algorithm, we described the contact between the pier and the vehicle. All parts of the vehicle are assigned as a master parts set. All parts of the pier are assigned as a slave parts set. The static and dynamic coefficient of friction was set to represent the coefficient of friction between concrete and steel (ElTawil2004). Displacements, shear forces, and moments at various heights along the length of the pier were recorded. Using a set of nodes and volumes, we identified sections of the column every 500 mm along the length of the column and obtained such results.
The impact force of generated between the
vehicle and the pillar members was also recorded. The time course of kinetic energy, internal energy, total energy, and hourglass energy during the simulation was recorded.
6.2.5. Model Summary
A total of 75,952 nodes and 69,373 elements make up the vehicle and pier model. The column model, including the foundation and soil source, consisted of 37,003 nodes and 34,020 elements. The pier model had 2,664 beam elements, 30,960 solid elements, and 396 individual elements. The height of the element along the Z axis was set to 50mm. As shown in Figure 6.3, due to the unique structure of the circular cross section of the column, the mesh size of the column elements ranged from 30 to 75 mm. The same mesh was used for three columns with different diameters. Connections between different parts of the model were guaranteed by putting the nodes together in the same place.
6.3. VEHICLE IMPACT RESULTS
6.3.1. Visual Response Due to Vehicle Collision
A total of 27 analyzes were performed.
Three column diameters with three different tire clearances at three vehicle impact speeds. Divide the result by the diameter of the pier to observe the failure mechanism caused by the vehicle collision at 100ms.
The following results show the effects of tire clearance and concrete confinement with Mander and others.
(1988) updated the concrete strength of various columns with different stirrup intervals as shown in Table 01. It can be seen that when the maximum stirrup spacing is 300 mm, the increase in concrete strength due to inclusions is minimal. Reducing the stirrup spacing to 50 mm increases the strength of the enclosed concrete by 25% to 50%.
Necking of core concrete plays an important role in the ability of columns to effectively withstand impact forces. This can be confirmed by the hit result below.
Reducing the distance between the rings increases the strength of the constrained concrete in the core and increases the shear strength of the columns.
Table 6.1 Confined concrete strength (MPa) for various piers and hoop
spacing
The 600 mm column had the lowest structural rigidity of the column in this study. As a result, a significant amount of impairment was observed in these columns. Figure 6.5 shows the results shown by the 600 mm arrows with ring spacing of 300, 150, and 50 mm. It can be observed that as the impact speed of the vehicle increases, so does the damage to the pier. This is a correct observation. As the vehicle speed increases from 55km/h to 120km/h, the kinetic energy of the vehicle increases quadratically and is transmitted to the pier after a collision. The distance between the stirrups allows you to observe the effects of pillar concrete shrinkage at different impact velocities.
Increasing the stirrup spacing reduces the critical strength of the concrete core, reduces the shear strength, and increases the damage of where the columns connect to the pile head.
Figure 6.5. Collision response at 100 ms for 600 mm diameter pier with
different hoop spacing at vehicle impact velocities of 55 (left), 80
(center), and 120 km/h (right)
Figure 6.6 shows the results that occur in columns with a diameter of 900 mm with ring spacing of 300, 150, and 50 mm.
Damage from vehicle impacts of 55 km/ h and 80 km/h was minimal and there was no significant erosion of concrete elements. The impact of the vehicle at 120 km/h caused a serious breakdown at the foot of the pier. This type of breakage is expected because large changes in shape produce high shear forces. It has been observed that the greater the distance between the stirrups, the greater the damage and the less effective the containment of the concrete core.
Figure 6.6 Collision response at 100 ms for 900 mm diameter pier with different hoop spacing at vehicle
impact velocities of 55 (left), 80 (center), and 120 km/h (right) In this study, piers with a diameter of 1,200 mm had the most important structural stiffness of the piers. As a result, there were no significant screw connections on these pillars, either between different tire distances or because of the speed of the car's effect.
This is because the higher the rigidity of the pillar, the greater the effect that the pillar can absorb. Figure 6.7 shows the results of a car collision with pillars with diameters of 1200 mm and tire clearances of 300, 150 and 50 mm.
Figure 6.7 Collision response at 100 ms for 1,200 mm diameter pier with different hoop spacing at vehicle impact velocities of 55 (left), 80
(center), and 120 km/h (right) As a end result of automobile collisions, fracture modes have been determined:
bending fracture and shear fracture.
Vertical rebar breakage is an indication of bending breakage in which the tensile strain tears the concrete from the weight and the tensile pressure is tolerated mainly with the aid of using the rebar.
Plastic hinges are fashioned in regions in which in depth inelastic deformation takes place because of stresses that exceed the rated second energy of the shape. As proven in Figure 6.5, examples of bending rupture and plastic hinge formation are determined on columns with ring spacing of fifty, a hundred and fifty, and three hundred mm and diameters of six hundred mm at effect velocities of eighty and one hundred twenty km/h. Bending fracture become additionally determined at an effect pace of one hundred twenty km/h on columns with a diameter of 900 mm and a hoop spacing of three hundred mm. Three plastic hinges have been fashioned: the effect point, the bottom of the pillar, and the pinnacle of the pillar. Diagonal tensile cracks thru the concrete center are a signal of shear failure. In the occasion of shear failure, the tensile pressure of concrete creates cracks earlier than the overall bending energy of the shape develops. Examples of shear fractures are
determined on piers with diameters of 900 mm, ring spacing of fifty and a hundred and fifty mm, and effect velocities of one hundred twenty km/h. Shear fractures have been additionally determined on pillars with a diameter of six hundred mm and ring spacing of fifty and a hundred and fifty mm at an effect charge of fifty five km/h. Oblique shear failure takes place close to the pier and spreads diagonally over the whole go section. No screw ups of any type have been determined at the 1,2 hundred mm diameter stanchions uncovered to the automobile collision. The tension of those pillars become massive sufficient to soak up the kinetic electricity implemented with the aid of using the transferring automobile, no matter the effect pace of the automobile or the clearance of the tires, without inflicting any substantial damage.
6.3.2. Energy Conservation
Figure 6.8 shows the energy distribution at impact velocities of 55, 80, and 120 km /h for pillars with a diameter of 1,200 mm and a bracket spacing of 300 mm. In general, the energy distribution curves of all columns analyzed in this study appear to be similar, as shown in Appendix A.
Energy saving is one of the important indicators of model stability, the simulation results are useful and the energy is effectively transferred throughout the system.
The total energy of the system should be kept fairly constant. The kinetic energy is converted into internal energy, suggesting that the kinetic energy of the moving vehicle is converted into internal energy associated with vehicle deformation and pedestal displacement.
Figure 6.8 Energy distribution of the 1,200 mm pier with 300 mm hoop
spacing
The maximum kinetic energy of the vehicle impact simulation was confirmed by Equation 01 and calculated as 941, 1,990, 4,480 MJ at impact velocities of 55, 80 and 120 km/h. The maximum kinetic energies of the simulation were 1,030, 2,075 and 4,555 MJ at impact velocities of 55, 80 and 120 km/h, respectively. The kinetic energy obtained from the simulation was within 10% of the calculated value. The simulation was well correlated with the expected kinetic energy values.
The main concern of energy saving is to ensure that less than 10% of the total energy comes from hourglass energy (Bala and Day 2004). Table 02 shows the ratio of the hourglass to the energy of the entire system for columns with diameters of 900 mm and 1,200 mm. Based on the energy distribution from the results, the energy of the hourglass accounts for a very small proportion of the total energy, between 0.2% and 4.9% of the total energy. Therefore, the can be assumed that the hourglass control is working properly and the sub-integrated hourglass with solid elements is minimized.
Table 6.2 Percentage of hourglass to total system energy
6.3.3. Resultant Impact Force
During the analysis, the resulting impact force at the interface between the pillar and the vehicle element was recorded.
Figure 6.9 shows the impact force-time curve of a column with a diameter of 1,200 mm and a stirrup interval of 300 mm. The impact force-time curves obtained from all the supports examined in this study are shown in Appendix B. It can be observed that the dynamic peak force increases as the impact speed of the vehicle increases. The duration of the peak impact force decreases as the impact speed of the vehicle increases.
Figure 6.9. Resultant impact force time history at various impact velocities for
1,200 mm diameter pier with 300 mm hoop spacing
Table 03 summarizes the resulting impact forces. This table shows the dynamic peak force (PDF) and the average glide peak of the resulting impact force of 10 ms at over time between the vehicle
and the pier. Note that the 10 ms moving average force is significantly smaller than the peak impact force. Only at low impact velocities (55 km/h for all column diameters, 80 km/h for 600 mm columns), the design impact force exceeds the moving average of 10ms. This underscores the fact that bridges designed according to AASHTO's recommendations will be severely damaged at higher impact velocities. The 10ms floating peak serves as a more representative value that can be used to determine the force that the column can withstand over a period of time as the structure responds to impact loads. A moving average window of 10 ms was considered to accommodate the duration of the peak impact force.
Table 6.3 Summary of peak dynamic and 10 ms moving average forces
It has been observed that the PDF increases as the impact speed of the vehicle increases. The PDF with a vehicle collision speed of 55 km/h was about 2,000 kN, which was almost constant across all three pillar diameters. At medium to high impact velocities, the PDF increased with column diameter.
Equation 06 shows that the impact force is proportional to the stiffness of the pier and the displacement due to the collision.
The larger the diameter of the column, the larger the PDF, and the larger the rigidity k of the structure, the larger the impact force fc. As the impact speed increases, the PDF will increase as the vehicle's
kinetic energy increases. The larger the frame spacing, the less rigid and the more flexible the structure, and the less flexible the PDF.
6.3.4. Displacement, Shear, and Moment
The large mass at the top of the column represents the weight that the superstructure puts on the column. The mass is not limited and can move and rotate freely. However, the huge mass has a large inertia and can withstand a large lateral displacement. When a vehicle collides with a pier, the displacement at the base of the pier is limited by the interaction of the soil structure of the deep pile foundation. At the top of the column, lateral displacement is limited by the large inertia of the mass of the superstructure. Figure 6.10 shows an example of a lateral displacement of a column with a diameter of 600 mm and a tire clearance of 150 mm in a 55 km / h vehicle collision at various time steps.
This figure shows the propagation of lateral displacement along the length of the column during a collision event. The lateral displacement along the length of the pier for each simulation is shown in Appendix C. Table 04 summarizes the maximum positive and negative lateral displacements of the support. The positive shift occurs in the direction of the applied impact. It was observed that the maximum positive displacement of the column occurs at the impact point and the maximum negative displacement occurs at the top of the column. Pillar displacement has been observed to increase with increasing impact speed and tire clearance. This is because at the same impact force, as the tire clearance decreases, the structure becomes less rigid and the pillar displacement increases. It has also been observed that reducing the diameter of the pier increases the lateral displacement. There is good reason for the smaller column diameter, which significantly reduces the moment of inertia and lateral stiffness.
Figure 6.10. Lateral displacement of the 600 mm diameter pier with 150 mm hoop spacing at a 55 km/h impact
velocity at different time steps Table 6.4 Summary of maximum
positive and negative lateral displacements in the various piers
7 CONCLUSIONS
Vehicle collisions with piers can cause serious damage to bridge components and lead to catastrophic failure of the entire bridge. The damage caused by a vehicle collision can have a devastating impact on the community by closing major transportation routes, paying for repairs, and losing lives during the event. The design specification uses equivalent static loads to design the impact load event for the vehicle. Studies have shown that design specifications underestimate the force of the generated during a collision event, suggesting that alternative design methods need to be developed. Previous studies have outlined various methods of
validating and developing finite element models that simulate collisions with vehicle columns. Chapter 2 of Chapter 2 showed that a vehicle collision with a pier can pose a serious threat to the country's infrastructure. The interactions and construction forces created by vehicle- column collisions are not fully understood by researchers. Large-scale experiments are expensive, so many researchers use finite element codes like LSDYNA to study collisions with vehicle columns. Recent experiments have changed the design specifications, suggesting that many of the horses manufactured prior to the change did not meet the design criteria.
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