The author describes observations of shear wall performance in severe earthquakes in which modern reinforced concrete buildings stood the test of violent shaking, starting with the Chilean earthquake of May 1960 through most of the subsequent strong earthquakes, up until the Armenian earthquake of December 1988. Despile the excellent behavior of shear wall-type concrete structures as compared to concrete frame-type structures, building codes continued, up until the last decade, to give preference to concrete ductile frame structures (which are subject to higher distortions) while placing a substantial penally on the use of shear walls. This code approach was due to the lack of experimental and analytical background information on shear wall behavior. While a large body of information on shear walls accumulated during the 1980s, still more experimental and analytical studies are needed to create a solid basis for a rational seismic design approach. The availability of such information should encourage a wider use of shear walls for earthquake resistance

Performance of Buildings With Shear Walls in Earthquakes of the Last Thirty Years

https://www.eng.buffalo.edu/~bruneau/Engineering%20Structures%202011%20El-Bahey%20Bruneau.pdf

Buckling restrained braces as structural fuses for the seismic retrofit of reinforced concrete bridge bents

Structural fuses, easily replaceable sacrificial elements to dissipate seismic energy while preventing damage to the gravity load-resisting structural system, are proposed as part of a multicolumn accelerated bridge construction (ABC) pier concept. Different types of structural fuses are investigated to compare the effect of each on ABC bridge bents. The piers of a three span-continuous bridge prototypes having two twin-column pier bents were designed using double-composite rectangular columns and structural fuses. Two corresponding 2/3-scale models were developed and were subjected to cyclic quasi-static tests. For the first specimen, steel-plate shear links (SPSLs) were installed between the columns as a series of structural fuses. Testing was performed, first up to a drift corresponding to the onset of columns yielding to investigate the effectiveness of adding the fuses in dissipating the seismic energy, then up to failure of the composite columns. The second tested specimen has buckling restrained braces (BRBs) as a series of structural fuses between the columns. The BRBs were then removed, and a cyclic test of the composite bent continued until failure of the columns. Both specimens exhibited stable hysteretic behavior, with the structural fuses also increasing stiffness and strength of the bent. Individual testing results for the SPSLs with various geometries and boundary conditions are then presented.

/pdf/bridge-piers-with-structural-fuses-and-bi-steel-columns-i-24cx6kdvle.pdf

Bridge Piers with Structural Fuses and Bi-Steel Columns. I: Experimental Testing

New performance-based seismic design method for structures with structural fuse system

Passive energy devices (PED) are useful to enhance structural performance by reducing seismically induced structural damage. Metallic dampers are one such PED. When they are designed such that all damage is concentrated on the PED devices, allowing the primary structure to remain elastic, they can be defined as structural fuses (SF). A comprehensive parametric study was conducted to investigate the structural fuse concept, and to identify combinations of key parameters essential to ensure adequate seismic performance for structural fuse systems. Non- linear time history analyses were conducted for several combinations of parameters, chosen to cover a range of feasible designs. Viable combinations of parameters are identified and used to provide guidelines to design and retrofit systems using Buckling-restrained Braces (BRBs), Triangular Added Damping and Stiffness (T- ADAS), and Shear Panels (SPs), examples of metallic dampers working as structural fuses. Studies focus on the application of the structural fuse concept to single- and multi-degree-of- freedom systems. Tables, many illustrations, and references are included.

Analytical Investigation of the Structural Fuse Concept

An alternative to the empirical approach to earthquake-resistant design of buildings is proposed and illustrated with a design example. Instead of strengthening every member to resist deformation under earthquake loads, the suggested approach deliberately makes some members, mostly beams, weaker, so that they will yield in a controlled fashion during an earthquake. Yielding beams dissipate energy, reducing stress on the more crucial columns and walls. Carefully selected earthquake accelerograms are used as loading, and dynamic inelastic response history analysis is used to determine member forces and deformations.

The Structural Fuse: An Inelastic Approach to Earthquake-Resistant Design of Buildings

On March 4, 1977, 35 buildings collapsed during a severe earthquake (7.2 on the Richter scale) in Bucharest, Romania. Thirty-two of the 35 were older structures, erected before World War II, before seismic design was considered. After World War II, construction began with cast-in-place concrete, rigid frame structures having clay masonry infill walls and partitions; some have since been stiffened with shear walls. With few exceptions, multistory cast-in-place concrete structures built during the past 25 years had enough strength and stiffness to withstand the earthquake, More recently, 70,000 dwelling units have been built using precast large-panel construction in buildings up to nine stories high. Precast buildings designed for earthquake resistance withstood the earthquake with little distress.

Modern Concrete Structures Survive Romanian Earthquake

In the late 1950’s and early 1960’s, the height of concrete buildings jumped from 20 to 60 stories. During the same period, architects introduced the use of exposed columns that are subject to thermal movements. Such changes made it necessary for the designer of high-rise buildings to consider column length changes due to elastic stresses and creep caused by gravity loads, drying shrinkage, and temperature variations of exposed columns. While column length changes within a single story may be minor, they are cumulative. When multiplied by a large number of stories, they become substantial. The total shortening affects such nonstructural elements as pipes and elevator rails attached to the concrete. Cladding details are also affected by overall changes in column lengths. Structural effects are caused by differential movements only and not by total movements; they are moments induced into the forcibly distorted slabs or beams and the accompanying moments in the columns. In the 1960’s, the structural solutions for effects of shrinkage and creep required extensive longhand computations. A procedure for determining elastic or inelastic column length changes in tall structures has now been updated, computerized and make applicable to concrete, steel and composite structures. The updated procedure separately considers elastic and creep shortenings due to gravity loads and shrinkage shortening. While elastic and creep deformations depend upon loading history, member size and reinforcement, the shrinkage component is independent of loading and depends on member size and on reinforcement. Time and material properties are important variables in all computations of shortening.

Mark Fintel

Papers

The Structural Fuse: An Inelastic Approach to Earthquake-Resistant Design of Buildings

Modern Concrete Structures Survive Romanian Earthquake

High Rise Design: Accounting for Column Length Changes