Incremental Dynamic Analyses Of Steel Moment Resisting Frames With Superelastic Viscous Dampers

Steel frame structures are made as the name suggest from steel, the material is strong and flexible. When weight is added it bends without cracking. Another characteristic of steel is that its plasticity or ductility, meaning that when force is added it won’t crack however it will lose shape therefore giving warning for people to evacuate the building. A disadvantage of steel is that is loses strength when subject to fire. Studies have shown that it can loose up- to half its strength when subject to fire, therefore making it imperative to cover the steel with boards or spray on.

This document’s purpose is to look for various available bracings used in a steel structure, which can be applied during construction to prevent the building from succumbing to the damage occurred due to the lateral movement, vertical movement, oscillatory movement, etc. caused by the seismic forces such as earthquake force and also forces such as wind load acting laterally.

Each separate truss (of the dimensions 920x5x50mm) consisted of a Pratt truss with nine diagonal members on each side of the centre. The model was tested in sufficiently isolated condition by tutors. It successfully passed the initial weight test, and satisfactorily resisted horizontal forces. Once fitted onto the testing rig, loads were applied and increased incrementally. Slight deformation was observed before failing at 12.5 kg, at which force a collection of members failed in succession, concluding the test.

Furthermore, when the millennium bridge opened within the first weekend around 100,000 people had crossed the bridge. Due to such heavy traffic, this lead to something called resonance. Resonance is when the input vibrations frequency coincides with the natural frequency of the structure itself, causing large deflections to develop. The issue caused the bridge to undergo a swaying movement; hence led to its closure. After extensive research and analysis, it was found that the movement was caused by synchronized pedestrian footfall. To prevent this there were two options taken into account the lateral stiffening and the damping; both were used in order to increase the natural frequency of the structure so it did not match the footfall. In addition structures called fluid-viscous dampers and tuned mass dampers were installed to control both horizontal and vertical movements.

The Maverick Center appears to be built with things like steel beams and might hold up considering the shaking might damage buildings built with masonry in that area. The biggest risk would

Clark Eldridge, an engineer from Washington State, had designed a trusted, conventional suspension bridge that would cost eleven million dollars. He requested that amount from the Federal Public Works Administration. However, Leon Moisseiff developed a design modification that would make the total cost of building the bridge much less- only eight million dollars. He swapped out the twenty-five feet long sturdy trusses as the form of support for the much cheaper alternative of 8 foot long girders, which were proven to be an insufficient form of support from the collapse of this bridge. His design accounted for an overall thinner bridge; and since his was the cheaper option, it was chosen for construction. However, the width of the bridge in comparison to the length, as well as the absence of trusses which would provide stability, are both part of Moisseiff’s “cost-effective”, yet impractically unsafe design. Since his design was flawed, he is mainly responsible for the bridge collapse. However, the board of engineers who approved his design are also partially responsible for the bridge collapse, as this unsafe design was allowed to be constructed. Meanwhile, it is imperative to remember that theories on aerodynamics were not fully developed as of the time that this bridge was constructed. Therefore, the full effect of oscillating forces was not properly accounted for due to the

Springs and other building materials are used to help save lives in earthquake prone areas. Scientist use a variety of different materials spanning from shock absorbers to springs. Scientists put springs under building that allow the buildings to sway but not topple over. Scientist tell builders to put steel bracing supports around or in the walls of buildings in between these are shock absorbers which stop the vibrating from going up the building. These are made of steel which are strong and don’t move a lot. Building materials need to be strong and flexible so that when an earthquake occures it won’t break. Steel ball bearings will move the platform and themselves but they will not move the house this helps the house

There are other ways to improve buildings to reduce the impact of earthquakes. In some Japanese buildings, there’s a base isolation built. The “Base Isolation” is a system that is made of steel disks. These steel disks are made of soft materials to soften the transmission of seismic movement from the ground

The main addition that I made to the house is the addition of base isolators. These act like springs under the house, absorbing most of the vibrations that

The FHWA has recommendations for new designs and existing construction. Some of the recommendations for new designs are: Use continuous spans rather than simply supported spans; this will reduce the need for expansion joints and thus minimize the potential for span separation. A side benefit of this practice will be a reduction in joint maintenance costs. And, use earthquake-protective systems (e.g., seismic isolation), where appropriate, to minimize the seismic demand on bridge members.

There are only a very few limitations in the use of plate girders. Compared with trusses they are heavier, more difficult to transport and have larger wind resistance. The provision of openings for services is also more difficult. The low torsional stiffness of plate girders makes them difficult to use in bridges having small plan radius. Plate girders can sometimes pose problems during erection because of concern for the stability of compression

The comparison of measurement and prediction of prestress losses in prestressed members is highly documented in literature. Hale et al. (2006) studied the prestress losses behavior of girders subjected to increased fiber stresses. They concluded that the previous AASHTO LRFD Specifications equations (2004) overestimated the prestress losses by roughly 50%. It was found that the NCHRP Report 496 (Tadros et al., 2003) equations predicted the losses to within an average of 6%. Currently, there have been quite a few investigations on empirical models for prestress losses for HSC. In a study conducted by Kowalsky et al. (2001) on several HPC bridge girders in North Carolina to determine the prestress losses of HPC girders. The researchers found shrinkage losses were a small component of the overall prestress losses and that the elastic shortening and creep losses were the main contributors. These larger than expected losses from elastic shortening and creep were because of a predicted modulus of elasticity that was higher than actual. The total prestress losses ranged from 12.9% to 19.1% of the initial jacking stress. In an investigation conducted by Tadros et al. (2003), seven full-scale bridge girders were instrumented in Washington, Texas, Nebraska and New Hampshire to determine the prestress losses of HPC girders. The total prestress losses measured were found to be lower than the AASHTO LRFD (1998) model. Modified expressions were proposed to AASHTO and later adopted in

The Tacoma Narrows Bridge was designed for a wind speed of 100 miles per hour and a static wind pressure of 30 pounds-force per square foot but unfortunately the bridge failed at a wind speed of less than half and a static wind pressure of one-sixth (Delatte, 2009). This phenomenon raises a big question mark on how this is possible. At first, resonance was suspected to be the main cause of the bridge failure (The New York Times, 1940). After some proper research and thorough investigations by engineers, they came up with several theories on how did the bridge collapse. The primary cause of the collapse lies in the general proportions of the bridge and the type of stiffening girders and floor. The ratio of the width of the bridge to the length of the main span was so much smaller and the vertical stiffness was so much less than those of previously constructed bridges that

One of the most influential engineering discoveries in the past century was the ill-fated Tacoma Narrows Bridge. “Galloping Gertie” as she was known to local residents, the massive Washington state suspension bridge shook, rattled and rolled its way into the history books. Legendary in its time, the Tacoma Narrows Bridge held many records and drew tourists from around the world in its short life. However, the famous bridge is not known for its creative engineering or speedy construction, unfortunately the bridge was destined to fail. That failure in turn changed the way every building is constructed today as well as further man’s understanding of physics and the forces of nature. In this paper we

Introduction: Structural systems for tall buildings have undergone a dramatic evolution throughout the previous two decades and into the 2010s. Developments in structural form have historically been realized a response to emerging architectural trends in high-rise building design. The development of the original tubular systems for tall buildings was indeed predicated upon an overall building form of constant or smoothly varying profile [1]. As the number of different high-rise structures in existence expands every year, there is an increase in the possibility of damage due to earthquake or other hazards. In the event of such damage it is important to be able to correlate damage intensity with the particular tall building system used. Of the various alternatives, a framing-oriented scheme is selected as a means of classifying structural systems. The fundamental systems within it are bearing wall, core, tube, and frame, together with the appropriate mixtures of these systems. For a proposed building there is no right or wrong way for a structure to carry gravity loads to the foundation or resist lateral loads. However, there are structurally efficient solutions, economic solutions and other radical, unique, and challenging solutions [2]. Tall buildings are highly sophisticated engineering projects. Due to the complexity of the structures, the most advanced engineering design techniques are needed in