The most advanced pavement structural design uses a mechanistic-empirical method approach. Unlike an empirical approach, a mechanistic approach seeks explaining phenomena by reference to physical causes. In pavement design, the phenomena are the stresses, strains and deflections within a pavement structure, and the physical causes are the loads and material properties of the pavement structure. The relationship between these phenomena and their physical causes is typically described using a mathematical model.
Various mathematical models we can use.
Along with this mechanistic approach, empirical elements are used when defining what values of the calculated stresses, deflections strains and result in pavement failure.
The relationship between physical phenomena and pavement failure is described by empirically derived equations that compute the number of loading cycles to failure. The basic advantages of a mechanistic-empirical pavement design method over a purely empirical one are:
* It can be used for both existing pavement rehabilitation and new pavement construction.
* It accommodates changing load types.
* It can better characterize materials.
* It uses material properties that relate better to actual pavement performance.
* It provides more reliable performance predictions.
* It better defines the role of construction.
* It accommodates environmental and aging effects on materials.
A mechanistic-empirical approach can also accurately characterize in situ material (including subgrade and existing pavement structures). This is typically done by using a portable device (like a falling weight deflectometer) to make actual field deflection measurements on a pavement structure to be overlaid. These measurements can then be input into equations to determine the existing pavement structural support and the approximate remaining pavement life. This allows for a more realistic design for the given conditions.
So, expert knowledge is required to use mechanistic-empirical approaches; a pavement design expert should be consulted if you are considering its use
السبت، 9 أبريل 2011
الأربعاء، 6 أبريل 2011
Structural engineering is a branch of civil engineering, and its applications are extremely diverse
Superman may be can leap tall buildings with a single bound, but the tall buildings wouldn't be there if it weren't for structural engineers.
Structural engineering is a branch of civil engineering, and its applications are extremely diverse. A great deal of what structural engineers do involves designing things to be built, and then helping to build them: buildings, tunnels, bridges, towers. "Probably 75% of our clients are architects," says Scott McConnell, project manager at the engineering firm of Schoor DePalma in Manalapan, N.J. "Most of what I do is building design. The architect comes up with a building design, and then it's the structural engineer's responsibility to fit the structure to the architecture, and decide on what structural system is best suited to that particular building. We design the beams, the columns, the basic members to make the building stand up."
But a structural engineer might also be involved in the demolition or dismantling of a structure, either permanently or in order to repair it. For both of these processes, they need to know about the forces that act on structures—the stresses put on a bridge by heavy traffic or on a high building by strong winds, or on any structure by seasonal temperature changes or earthquakes.
Structural engineers also inspect buildings, both during and after construction, and oversee the use of the concrete, steel and timber of which they are made. They must also be aware of both obvious and inobvious uses for the structures and how these uses affect its design. "For example, if they're putting in sensitive computer equipment or doing pharmaceutical work, you have to use a floor system that's very stiff and doesn't move much," explains McConnell.
Like all engineers whose work may affect life, health or property, new structural engineers go through a rigorous training process during their first few years of work. This training involves several years of work experience under the supervision of experienced engineers and one or more state examinations, and results in a license as a Professional Engineer (P.E.). This is one profession where an advanced degree is more of a necessity than an option.
"My advice to students is that if they're really committed to structural engineering, they should get their master's degree in structural engineering or civil engineering as quickly as possible," says Terry Blackburn, Ph.D., senior vice president and head of the structural department at Schoor DePalma. "The basic courses at the undergraduate level just can't touch on all the necessary aspects of structural engineering. Your advance in the profession is greatly impaired by not having a master's degree."
Along with technical know-how, a structural engineer needs a host of other skills to be able to interact with professional and nonprofessional co-workers and clients. "Sales ability, public speaking and time management are very important when we have to make contact with clients," says Blackburn. "And problem resolution is a skill that isn't typically taught in engineering schools. But when there's an enormous amount of work that costs a lot of money, that is going on very rapidly, and there are problems, then the problems have to be resolved as quickly as possible."
This branch, like other civil engineers, frequently hold the lives of others in their hands, a point that Blackburn says should be explained early and often to would-be structural engineers. "I know I was very surprised at the amount of responsibility that is piled on an engineer," he says. "It's enormous. You hear about things like the Kansas City skyway collapse. Someone is still personally blaming himself today for that. He has to live with that... It's almost heart-stopping when you get a telephone call from a job and something's gone wrong. I think that at some point in the career of most engineers, it just dawns on them, all the responsibility they've assumed over the years—not just the professional responsibility, but the personal liability, too."
Structural engineering is a branch of civil engineering, and its applications are extremely diverse. A great deal of what structural engineers do involves designing things to be built, and then helping to build them: buildings, tunnels, bridges, towers. "Probably 75% of our clients are architects," says Scott McConnell, project manager at the engineering firm of Schoor DePalma in Manalapan, N.J. "Most of what I do is building design. The architect comes up with a building design, and then it's the structural engineer's responsibility to fit the structure to the architecture, and decide on what structural system is best suited to that particular building. We design the beams, the columns, the basic members to make the building stand up."
But a structural engineer might also be involved in the demolition or dismantling of a structure, either permanently or in order to repair it. For both of these processes, they need to know about the forces that act on structures—the stresses put on a bridge by heavy traffic or on a high building by strong winds, or on any structure by seasonal temperature changes or earthquakes.
Structural engineers also inspect buildings, both during and after construction, and oversee the use of the concrete, steel and timber of which they are made. They must also be aware of both obvious and inobvious uses for the structures and how these uses affect its design. "For example, if they're putting in sensitive computer equipment or doing pharmaceutical work, you have to use a floor system that's very stiff and doesn't move much," explains McConnell.
Like all engineers whose work may affect life, health or property, new structural engineers go through a rigorous training process during their first few years of work. This training involves several years of work experience under the supervision of experienced engineers and one or more state examinations, and results in a license as a Professional Engineer (P.E.). This is one profession where an advanced degree is more of a necessity than an option.
"My advice to students is that if they're really committed to structural engineering, they should get their master's degree in structural engineering or civil engineering as quickly as possible," says Terry Blackburn, Ph.D., senior vice president and head of the structural department at Schoor DePalma. "The basic courses at the undergraduate level just can't touch on all the necessary aspects of structural engineering. Your advance in the profession is greatly impaired by not having a master's degree."
Along with technical know-how, a structural engineer needs a host of other skills to be able to interact with professional and nonprofessional co-workers and clients. "Sales ability, public speaking and time management are very important when we have to make contact with clients," says Blackburn. "And problem resolution is a skill that isn't typically taught in engineering schools. But when there's an enormous amount of work that costs a lot of money, that is going on very rapidly, and there are problems, then the problems have to be resolved as quickly as possible."
This branch, like other civil engineers, frequently hold the lives of others in their hands, a point that Blackburn says should be explained early and often to would-be structural engineers. "I know I was very surprised at the amount of responsibility that is piled on an engineer," he says. "It's enormous. You hear about things like the Kansas City skyway collapse. Someone is still personally blaming himself today for that. He has to live with that... It's almost heart-stopping when you get a telephone call from a job and something's gone wrong. I think that at some point in the career of most engineers, it just dawns on them, all the responsibility they've assumed over the years—not just the professional responsibility, but the personal liability, too."
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