Early attempts of optimised structural designs go back to the 1600s, when Leonardo da Vinci and Galileo conducted tests of models and full-scale structures [1]. A 1994`s review of structural optimization can be found in the study by Cohn and Dinovitzer [2], who pointed out that there was a gap between theoretical studies and the practical application in practice. They also noted the short number of studies that concentrated on concrete structures. A review of structural concrete optimization can be found in the 1998`s study by Sarma and Adeli [3].

The methods of structural optimization may be classified into two broad groups: exact methods and heuristic methods. The exact methods are the traditional approach. They are based on the calculation of optimal solutions following iterative techniques of linear programming [4,5]. The second main group comprises the heuristic methods, whose recent development is linked to the evolution of artificial intelligence procedures. This group includes a broad number of search algorithms [6-9], such as genetic algorithms, simulated annealing, threshold accepting, tabu search, ant colonies, etc. These methods have been successful in areas different to structural engineering [10]. They consist of simple algorithms, but require a great computational effort, since they include a large number of iterations in which the objective function is evaluated and the structural restrictions are checked.

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This research project addressed key needs for advancing the design of pile foundations in soil profiles that are susceptible to liquefaction and lateral spreading during earthquakes.

A series of large-scale dynamic centrifuge model tests were performed to study the behavior of single piles and pile groups in a soil profile comprised of a nonliquefied crust spreading laterally over a loose saturated sand layer. Detailed instrumentation and new interpretation and data processing procedures enabled fundamental measurements of soil-pile interaction behavior in the centrifuge tests. The measurements include the first available time histories of loads from nonliquefied surface soils and underlying liquefied soils during lateral spreading under realistic earthquake shaking motions. The identified behaviors that are important to design practice include: (1) peak lateral down-slope loads from the surface crust may be in-phase or out-of-phase with lateral loads from the deeper liquefied layers; (2) the peak lateral loads imposed on the pile caps by the laterally spreading ground included significant interface friction loads from along the sides and base of the pile cap; and (3) the lateral load versus relative displacement response of pile caps embedded in laterally spreading ground was much softer than predicted by relations derived for static loading conditions.
Monotonic pushover analyses based on limit pressures or on nonlinear p-y analyses with monotonic kinematic loading were evaluated against the centrifuge data. Guidelines for estimating the lateral spreading loads from both nonliquefied and liquefied layers were subsequently provided. Pushover design analyses using these guidelines and common relations for other input parameters produced predictions of peak pile bending moments and pile cap displacements that ranged from reasonable to conservative.
Nonlinear dynamic time-history analyses were also performed using dynamic p-y, t-z, and q-z materials that were developed and implemented in connection with this project. Example problems and initial comparisons to centrifuge test data of pile-supported structures in liquefying sand profiles demonstrate that these modeling methods can reasonably approximate the essential features of soil and structural response.
Downdrag loads on vertical piles in liquefied soil profiles were evaluated using an adapted version of the neutral plane concept, and a simple design guideline was subsequently recommended.

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The underground Rapid Transit System (RTS) stations and cut-and-cover tunnels are typically constructed by the “open-cut and bottom-up” method. In this method, the earth is excavated to the required depth with retaining walls and struts supporting the soil at the sides. Upon the completion of excavation to the required depth, the base slab of the underground structure is cast at the bottom-most level, followed by the side walls. Casting of concrete progresses upwards, level by level till the roof of the structure is completed. Ground is then backfilled and reinstated.

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The underground Rapid Transit System (RTS) stations and cut-and-cover tunnels are typically constructed by the “open-cut and bottom-up” method. In this method, the earth is excavated to the required depth with retaining walls and struts supporting the soil at the sides. Upon the completion of excavation to the required depth, the base slab of the underground structure is cast at the bottom-most level, followed by the side walls. Casting of concrete progresses upwards, level by level till the roof of the structure is completed. Ground is then backfilled and reinstated.

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Paramount Apartment Building
San Francisco, CA
Engineer: Englekirk Systems Development
Precast Engineer: Mid-State Precast, L.P

• 39-story, 691,000 sq ft
• Seismic Zone 4 structure
• Hybrid moment resisting frame
• Integrated seismic and architectural solution
• Reduced construction time and material costs

At 39 stories and 420 ft (128 m) high, The Paramount (located in San
Francisco, California) is the tallest concrete structure in addition to
being the tallest precast, prestressed concrete framed building in
Seismic Zone 4 (a double record).It is the first major high rise
building to be braced by an architecturally finished exposed precast
concrete ductile frame. The reinforcement used to create this seismic
ductile frame includes post-tensioning and high strength reinforcing
steel. All this represents a major milestone in the development of
precast/prestressed concrete. The building is basically an apartment
complex, although the lower floors accommodate retail space, vehicle
parking and recreational amenities. This article presents the design
considerations, construction highlights, research and development,
and code approval process that led to the realization of this structure.

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