Friday, 25 May 2012



The design of a building is a complex process that may involve the participation of professionals of different areas, such as architects, urban planners, structural engineers, and engineers of several other specialties (water and sewage, mechanical, electrical, etc.). It is usually considered that the seismic resistance is a responsibility of the structural engineer, and this view is consecrated in the legal framework of many countries. However, this view does not correspond to reality. 

Even though the structural design is the most important part of the project to ensure an adequate seismic performance, it can be shown that projects of other specialties, with particular emphasis to the architectural design, may also have a strong influence on the final result in what concerns seismic resistance. It is therefore important that engineers, architects and project coordinators have the assertiveness to establish the correct priorities when decisions need to be made to compatible different architectural and structural requirements. The attitude of just trying to force the criteria that suits better the interest of his/her specialty (unfortunately common) usually results of the inability to evaluate and judge the relative importance of the factors that should be considered in the best interests of the promoter and the public, this is, it results of selfishness and incompetence. 

In building design, seismic safety starts at the level of urban planning. Issues such as mapping areas of potential landslides or liquefaction, with restriction or stronger requirements for construction should be considered at urban plans. Problems of pounding between buildings due to slabs at different levels should, common in inclined streets, should also be addressed at this level. Since urban planning may also involve also contributions of engineers and architects, this is another field where assertiveness and cooperation between architects and engineers is necessary.


Mário Manuel Paisana dos Santos Lopes, graduated in Civil Engineering at Instituto Superior Técnico (IST), Lisbon, in 1982. He was awarded the Edgar Cardoso prize of that year, for the best student in the área of Bridges and Special Structures. In 1987 he got his MsC degree in Structural Engineering from IST and in 1991 he got his PhD in Earthquake Engineering from Imperial College of Science and Technology, London. Since 1991 he is assistant professor at the Civil Engineering Department of IST, having participated in numerous research projects and thought several subjects of structural engineering. He is author of several papers published in international journals and conferences. He has also participated in several projects of reinforced concrete buildings and bridges, as well as of other structures. He is a member of the Executive Committee of the Portuguese Society of Earthquake Engineering (SPES) since 1996, and in the framework of the respective activities, has organized several events to raise awareness to the seismic problem and wrote several documents on earthquake risk mitigation policies.



Cathedral of our Lady of the Angels, Los Angeles, California, (2002) Rafael Moneo 

Due to the complexity of today’s architecture, the architect must incorporate the numerous scientific and technological advances such as base isolation in order to integrate a creative, imaginative and safe synthesis. The use of base isolation has an influence on structural behavior as well as on other architectural variables such as morphology, functionality, aesthetics and economy, being able to reach innovative design limits in seismic prones. This research tries to contribute to the integration of Architecture and Seismic Engineering, analyzing the architectural implications involved in the use of seismic base isolation. The theoretical conceptual knowledge of structural architecture is essential to develop more efficient and adequate architectural models.


Almost two thirds of the earth’s crust is seismically active. Every year, more than 150,000 seismic movements strong enough to be perceived by round about one billion people who live in these regions subject to earthquakes occur. 

Among the different dangers that threaten the human beings, earthquakes are causes completely out of people’s control. They cannot avoid them. They can just take preventive measures against them to diminish their effects. 

The architect conceives and designs the building configuration (Arnold and Reitherman 1999 – Charleson 2008) and therefore influences on the seismic behavior of buildings. 

As a risky discipline, the Theory of Architecture must take into consideration the principles of seismic-resistant structural design and be updated with regard to the advances in the seismic protection technologies in the same way it does with regard to sustainability, resources consumption, recycling and others. 

Seismic base isolation is a great advance for engineering to diminish the effects produced by earthquakes in architectural works. But no many architects have a thorough knowledge about the possibilities offered by this technology, nor an adequate integration between both disciplines allowing new projects to take advantage of this technology. 

In the design of most of the new buildings with base isolation, architecture is restricted to solving detail problems, such as facilities, stairs, elevators, and the elements which may obstruct the free move of the building in the gap.


Conventional architectural design takes into account “an acceptable seismic risk” that may diminish the damage level in the building. It does not avoid damage. 

This means a conceptual, an attitude and a decision change at facing the problem. One change consists in controlling the damages by designing them though they are not eliminated. The other change pursues the drastic reduction by the use of new devices. The solution is very different and it requires an adjustment to changes, which enables a new conception of the damage reduction in the buildings when a seism occurs. 

In this way, new technologies of seismic protection have new applications creating a new architectural concept of Architecture. 

The methodology of seismic protection is recent, but the idea dates back a long time ago, although it was not possible to bring it to fruition. There have been precedents of different preventive measures, not all of them being equally effective in the light of the present knowledge. As a general rule they have been the result of any sad event of catastrophic magnitude. 

The Temple of Diana in Ephesus, described by Pliny The Elder (23 AD – 79 AD), confirms the human beings concerns about protecting their constructions by placing an interface between the foundations and the building. Fifty years ago, new materials helped to develop elements and the idea became true. The first building with base isolation was the school Pestalozzi in the ´60 in Skopje, Macedonia (Naheim and Kelly, 1999) and since then, the development and evolution of the concept have not stopped. 

Base isolation technology has been applied worldwide in numerous earthquakes, showing a structural performance that had never been reached before. 

2.1. Seismic Architecture 

Man is the cause and purpose of Architecture. Human being is unique. He needs to protect himself from natural and social threats. In older times he made it in caves till now that he has created skyscrapers. (Salvadori 1979) 

Architecture must be a protection system for the different elements which may put his life at risk. It must shelter the human being abandonment during his life. 

Seismic Engineering stands as an interdisciplinary branch of civil engineering and earth sciences, mainly aimed at mitigating the effects of the seismic threat. The complex requirements of seismic engineering directly influence architectural composition and concepts (Parducci 2007). 

Seismic Architecture is the combination of principles related to architectural design and seismic resistant engineering. It combines the necessary elements from both fields and establishes new conceptual interlinks in the field of architecture. 

Earthquake resistant construction requirements are often seen as a pressure on artistic freedom and a restriction on the architectural ideas coming from non-seismic areas in the world. 

Nevertheless, the main problem is not the restrictions but the lack of knowledge to develop seismic resistant structural designs according to an adequate, creative, innovative, audacious, safe and sustainable architecture. 

2.1.1. Architectural Variables 

Architecture is a science, enhanced by many other disciplines and knowledge. It is Theory and Practice. From the area of Architecture Theory, the starting point for analyzing the Architecture Variables, the ones defined as principals (Utilitas, Firmitas and Venustas by Marcus Vitruvius Pollio -Roman architect, writer, engineer and treatise writer from s1 b. C.), shall be taken. Over time, these variables evolved from the complexity acquired by the architecture. 

Venustas refers to beauty as an aesthetic element, the meaning and communication of a message. Utilitas means the function the work will be used for, the organization and distribution of the architectural areas and Firmitas represents the concepts of durability, firmness, stability, permanence, resistance and configuration, among others. Safety mentioned by Vitruvio refers to material and technical aspects of Architecture. 

With Engineering, it shares the “Firmitas” variable and thus there is a contact area where Architecture and Construcion join. Then, it is necessary to identify the common components so as to have a wider and more complex view of the architectural and structural design, which is critical in seismic areas. Figure 1

Figure 1: Integration of Seismic Architecture Disciplines

2.1.2. Seismic Architecture Variables 

Firmitas variable is the one representing the possibility to design in an appropriate way an Architecture that is suitable for seismic high risk areas, which adds base seismic isolation as a strategy of damage reduction. It becomes very important and must be present from the conception itself of the architectural design. 

From this approach, architecture, when it is inserted in its seismic context, receives external actions such as the earthquake, and must respond by means of internal actions. 

Then, the architectural work must have the architectural performance and the structural performance that are appropriate to support said work. Figure 2 

Figure 2: Interdependence of the Architectural Design with its Context

The analysis is performed by means of an interrelation between the three variables of the Seismic Architecture, which uses the Base Seismic Isolation, which will enable to evidence how the architectural design is optimized and enhanced. 

2.2. Analysis of buildings with Base Seismic Isolation 

The methodology which is applied for the analysis of buildings consisted of performing an identification of the more outstanding architectural implications of the works so as to discover the architectural potentialities arising as a consequence of the use of base seismic isolation in the architectural design 

The selection criterion of the building typology is regarding the use, either because the buildings have great people concentrations, or because their survival is vital to act upon emergency situations caused by the seismic movements. Typologies of Hospitals, which may be operative after an earthquake so as to help victims and of Temples, which may be used as both a shelter for people who are homeless or as emergency centers are important.

Then, business buildings were analyzed for its potential avant-garde architectural design, which exceeds the traditional design limitations.

2.2.1. Analysis of the Seismic Architecture variables and the architectural implications when using Seismic Isolation Hospital Typology Temple Typology Commercial Building Typology

Prada Boutique Aoyama, Japón(2003) Herzog and de Meuron


After performing the analysis of the typologies that are selected, the following conclusions of the variables of Seismic Architecture are obtained, and then, the importance of the economic variable arises. 

3.1. UTILITAS: Benefits regarding the functions increased by the use of ASB

. The optimization of the area of use is achieved, since it enables a better architectural exploitation. The degree of incidence or interference of the structure from the point of view of the use and distribution of the architectural space is lower. 

. The functions of the buildings after a severe seismic movement are kept operative. 

. The physical and psychological protection of the users by means of damage reduction is optimized. 

. The psychological trauma generated by the perception of an important seismic movement and the devastating experiences that are caused by the deadly effects of the earthquakes is reduced 

3.2. FIRMITAS: Benefits regarding the structure, increased by the use of ASB 

. It enables complex configurations which respond to the project needs. 

. The efforts and distortions in the structures with an optimal structural performance in case of severe seismic movements are reduced. 

. Damages of a building during a severe seismic movement are drastically reduced, both from structural and non structural elements, by means of the isolation interface. 

. The damage of the building contents is avoided (high-technology equipment, machinery, etc.) 

. Life and Architecture Protection are optimized 

. A better adaptation to the seismic determining factor with a demonstrated efficacy is reached. 

. It is possible to preserve the cultural patrimony, the meaning and identity which witness periods in time. 

3.3. VENUSTAS: Benefits regarding beauty, increased by the use of ASB 

. It enables configuration freedom that was not previously recommended for the traditional seismic-resistant design. 

. Potentiality of creative freedom in the aesthetic design of the works increases more and more. 

3.4. ECONOMY: Benefits regarding investment and maintenance of capital 

. A reduction of the initial cost of the work is achieved, if the structural design is taken into account from the beginning. 

. The investment is maintained in time. Costs which would entail a structural rehabilitation as a consequence of an earthquake would be decreased in an important way. 

. It also reduces the economic risks of the affected areas, since people keep their way of living and support. 

. Decrease of economic losses due to activity standstill in the event of a seismic movement. 

. The sustainable development in seismic areas is increased 

. The application of technology of seismic protection in real estate projects may come to be only 1 % of the total cost, when it is previously planned (De La Llera 2011). 

. Some benefits are difficult to translate into monetary values or are not always tangible, such as the mental ease. 


Buildings, besides of being more efficient, safe, functional and economical, may achieve new design prospects in seismic regions. The architectural-structural theoretical conceptual knowledge of the architectural implications of Seismic Architecture is essential to develop efficient and adequate architectural models. 

Seismic Architecture can thus provide a means of Passive Protection against a potential earthquake. For such purpose, it has to incorporate new technologies like base isolation, within its conceptual-theoretical knowledge and then use them as design tools in a vital, comprehensive protection system which will drastically reduce damages and human losses caused by an earthquake. 

Environment is protected thanks to the work preservation, a greater possibility of applying strategies for the development of Sustainable Architecture and the use of new materials that are not recommended for seismic regions, such as prefabricate materials. 

The use of this technology from the conception of architectural design will enable more savings than the ones obtained until now, and thus it optimizes the result of the public and private investment. 

Solving an architectural work which not only contributes to decrease the seismic vulnerability and the environmental problem, but also provides benefits gives the possibility of living together with our planet, of living a promising future. 


To my engineer friends for sharing their knowledge, in particular to engineers Juan Carlos de la Llera (Chile), José Inaudi (Cordoba, Argentina), Eng. Agustín Reboredo (Mendoza, Argentina) and to my e-mail consultant Andrew Charleson (New Zealand). 

To my colleagues, Miguel Tornello and Daniel Moisset de Espanés, who support me in this branch of architectural discipline 

To my friends Luis Matons Cañomeras, Juan José Marino and Julio Diaz Valentín who were a party to the knowledge adventure of the structural design. 


Arnold, C. and Reitherman, R. (1987) Configuración y Diseño Sísmico de Edificios, Editorial Limusa, México Bozzo, L. and Barbat, A. (2000) Diseño Sismorresistente de edificios: técnicas convencionales y avanzadas, Editorial Reverté S.A., Barcelona 

Charleson, A. (2008) Seismic Design for Architects outwitting the quake, Architectural Press, USA 

Dolce,M. and Martelli, A. and Panza, G. (2005) Proteggersi dal Terremoto: Le moderne tecnologie e metodologie e la nuova normative sismica, 21mo Secolo, Milano, Italia 

Higashino, M. and Okamoto, Editors, S. (2006) Response Control and Seismic Isolation of Buildings, Taylor & Francis, USA 

Naheim, F. and Kelly, J.M. (1999). Design of Seismic Isolated Structures: from theory to practice, John Wiley & Sons, United States 

Parducci, A. Editor (2007) La Sfida dell´isolamento sismico, EdA Esempi di Architettura, Numero Speciale Giugno 2007, Il Prato, Lombardia, Italia 

Popovic Larsen, O. and Tyas, A. (2003) Conceptual Structural Design: Bridging the gap between architects and engineers, Thomas Telford Publishing, London, Great Britain 

Salvadori, M.(1979) “BUILDING, The Fight Against Gravity”, Atheneum, New York Tedeschi, E. (1978) Teoría de la Arquitectura, Ediciones Nueva Visión, Argentina.

Bahaí Temple, Chile (proyecto) Hariri - Pontarini Architects

Tuesday, 8 May 2012


L. Teresa Guevara and Luis Enrique García


Captive-column and short-column conditions are a significant source of serious earthquake damage. These conditions originate in the architectural design of the building. For this reason, this paper first presents the architectural reasons why these conditions occur and explains in nontechnical language their detrimental effect on building response. The effects are presented from a multidisciplinary perspective—engineering, architecture, and construction—because their solution can only be achieved by an integrated approach to building design that recognizes the interaction of these three disciplines. 

The accidental modification to the original structural configuration leading to a captive column by restricting its freedom to deform laterally due to the presence of nonstructural elements that partially confine it is presented. The case of short columns subjected to earthquake effects is also discussed. Examples of damage due to these effects in numerous earthquakes are presented, and the architectural decisions leading to captive and short columns are reviewed. The structural explanation of the behavior is discussed. Experimental research related to short and captive columns is presented. Recommendations to handle this type of problem are given.


Earthquake damage reports, with few exceptions worldwide, present numerous cases of captive-column effect. Although the problem shows itself as damage to the column, the cause usually rests with nonstructural elements imposing a pattern of response to the earthquake motions different from the expected behavior of the column by itself without the nonstructural elements. The root of the problem of this mode of response is associated with each of the professionals involved in defining the location, dimensions, and structural properties of a column, each of them looking at it from their own professional perspective. Generally, the problem originates in the architectural design of the building. The best solution to the problem is to ensure that architectural designers and construction contractors understand the problem and avoid creating the condition.

Contractors need to understand the problem because frequently the condition is created after the building is occupied, when contractors add partial height walls between columns at the request of a building owner without the input of an architect or engineer. For these reasons this paper begins with a nontechnical explanation of the effects of these conditions and shows many examples of consequent damage. Engineers can use these examples to explain to architects, contractors, and owners the dangers of creating such conditions. The remainder of the paper provides the results of analytical and experimental research that provides a solid basis for why these conditions should be avoided. 

Captive- and short-column conditions can also be caused by initial design errors in the detailed configuration of structural elements. The conditions are more frequently caused by interaction of structural and nonstructural elements that has not been taken into account in the analysis and design of the structure, or by later insertion of nonstructural elements between columns that create the conditions. The term ‘‘non-intentionalstructural element’’ (Guevara 1989) was coined precisely to describe this situation. Harmful response can only be avoided by separating the nonstructural elements from the structure or by taking into account the interaction in the analysis and design of the building. 


The captive-column effect is caused by a non-intended modification to the original structural configuration of the column that restricts the ability of the column to deform laterally by partially confining it with building components. The column is kept ‘‘captive’’ by these components and only a fraction of its height can deform laterally, corresponding to the ‘‘free’’ portion; thus the term captive column. 

Figure 1 shows this situation. Frequently during analysis, the structural engineer does not take into consideration the effect of the nonstructural elements in the response of structure. In most cases the analysis and design of the column is performed using the total clear height of the column because it is common to act on the assumption that the structure is free to sway laterally without interacting with the nonstructural elements.

The apparently inoffensive character of the nonstructural elements causes this common error in judgment, leading to unexpected and undesirable effects, as illustrated in Figures 2 to 3. Architectural decisions based on functional or aesthetic aspects are the most common reasons for the creation of captive columns. 

The need for incorporating openings to the walls of a building in order to provide natural lighting and ventilation leads to partial lateral confinement along the height of the column by rigid elements, such as internal partitions, facades, retaining walls, and other elements. 

The column ends up having adjoining walls in all its height, except in the upper part where the opening is located. The length of the column that would be free to deform laterally is reduced from the vertical floor to ceiling distance to just barely the height of the opening, as shown in Figures 2 and 3. 

Location of High, Narrow Windows on Tall Windowsills 

Openings above the line of sight are used when there is a perceived need to provide lighting and ventilation while restricting visibility from one space to the other. This type of configuration is often found in school classrooms, storerooms, rest rooms, doctors’ consulting rooms, and so on. In these cases, the nonstructural walls are higher than the height generally allowed for normal windowsills, and in order to comply with ventilation and lighting regulations the high windows extend from column to column (see Figures 4 and 5). 

Although the strength of the nonstructural masonry walls may be lower than the strength of the column, in many cases, under lateral deformations, the resulting ‘‘nonstructural’’ walls are sufficiently stiff to affect the column behavior. The confinement provided by the nonstructural walls to the lower part of the column is so effective that usually damage to the short upper section of the column occurs before the confining wall fails. 

Figure 6 shows how, when the captive column fails, the beams and the slab displace laterally in relation to their original position, while the windows have disappeared with the slab now resting on the ‘‘non-intentional structural walls.’’ Figure 7 shows how, in the same school, the outer column of the corner frame deformed but did not collapse because it was not laterally restrained by the walls. 

Figures 8 to 10 show captive-column effect in the building of ‘‘Empresas Pu´blicas de Pereira,’’ Colombia, produced by the 23 November 1979 earthquake. Figure 10 illustrates an inner view of an undamaged captive column shown at the left edge of Figure 8. This column was subjected to the same lateral displacements but did not fail. In this specific case, the reason was that columns shown in Figures 8 and 9 were restrained by solid brick walls while the column in Figure 10 was restrained by walls built using much weaker clay tile block that failed at the interface without affecting the column. The captive-column effect was present only where the glass block failed.

Open Corridors in Building Complexes 

A partial confinement of the clear height of the column is also common in housing complexes built during the 1950s in numerous countries. In this type of building, the configuration that followed the architectural trend of the Modern Movement (International Style), the corridors are left open to the fac¸ade. Instead of employing light, transparent handrails, heavy and stiff partial-height parapets were used, thus forming a captive-column configuration (see Figures 11 and 12). Figure 12 shows column failures due to captive-column effect in an external corridor of a housing complex with the same configuration as the building in the previous figure. 

Buildings on Sloping Grounds 

The captive-column effect is also produced in structures built on sloping ground where columns supporting the first-story slab end up having varying clear heights, as shown in Figures 13 and 14. 

Partially Buried Basements 

The captive-column effect is present also when partially buried basements are employed. The common practice is to use retaining walls with the columns embedded in them up to the street level, with only a small part of the height of the column continuing up to the next story slab. These openings provide ventilation and natural lighting to the basement, as shown in Figures 15 and 16. 


Framing at mid-height of the column of horizontal structural elements such as slabs, beams, and girders divides the column in two segments, thus producing the shortcolumn case. Although the terms captive column and short column have been used interchangeably in the literature, the reasons that cause them are completely different. In the former case, as explained before, the column is affected by the presence of adjoining nonstructural elements. In the latter case the column is made shorter than neighboring columns by horizontal structural elements, such as beams, girders, stairway landing slabs, and ramps, that frame at mid-height of the column, as shown in Figures 17 and 18. 

Other possibilities of short-column adverse configuration appear in frames located at the transition in split-level structures where the frame has beams located at half the usual vertical clear height in order to support slabs at alternating sides. Short columns are also caused by having a story of the structure with all columns much shorter than neighboring stories. This situation appears at the foundation, where foundation grade beams interconnect columns above the footing, leaving a gap between the grade beam and the footing. 

A variant of this case of short columns is present when atypical clear height floors are employed for sanitary or mechanical reasons. Figure 19 shows the vulnerability of this configuration in the 10 October 1980 El-Asnam, Algeria, earthquake. Numerous buildings had a one-meter crawl space under the first floor called a ‘‘sanitary story’’ to install plumbing and provide ventilation under the first-floor slab. This configuration converts into short columns all columns of the frame at the sanitary story level, resulting in numerous buildings’ losing this story by failure of all columns. 


In the most common case of captive-column effect when the column is restrained by adjoined nonstructural walls, column and walls interact, restricting the lateral deformation of the column. The upper free column segment is then responsible for accepting the deformation that the full height of the columns was designed to sustain. To acquire some insight on the captive-column effect from the structural perspective, we can divide the effects on the frame—and its columns—into those caused by gravity loads and those caused by lateral forces. 

The deformations of the frame elements vary in shape and magnitude, as shown schematically in Figure 20 for gravity loads and lateral forces. The ends of a column in a frame subjected only to gravity load (Figure 20a) remain basically plumb, unless the frame is extremely irregular. In the case of lateral load (Figure 20b), the upper end of the column displaces horizontally with respect to the lower end a distance denominated story drift (D). The order of magnitude of the column lateral deformations is significantly less for gravity loads than for lateral load. In a schematic and simplified manner.

Figure 21 shows the deformations (d) with respect to the original position of the undeformed column, the internal forces of the element—flexural moment M, axial force P, and shear force V—and the moment diagrams for both cases of gravity loads and lateral forces. In the column that is part of a frame subjected only to gravity loads, Figure 21a, the lateral deformations of the column depend only on the magnitude of the applied moments and the flexural stiffness of the column (d 5de). For the column belonging to a frame subjected to lateral forces (Figure 21b), the lateral deformations of the column depend on the sum of two factors (d 5de1dd): the first one (de) relates in the same fashion to the flexural moments and the stiffness of the column, while the second one (dd) depends directly on the story drift (D). 

The story drift is a function of the stiffness of the story and the structure, the geometry of the frame, the mass of the structure, and the earthquake motion. The individual column flexural stiffness plays a minor role in the order of magnitude of the story drift. Technical literature is rich in procedures for obtaining the internal forces and the general deformations of the frame for both cases. The relationship between the internal flexural moments that act at the column ends and the shear force associated with them can easily be obtained through the application of equilibrium principle and disregarding the P-Delta effect that may be significant for large lateral deformations:

Thus, the shear force V corresponds to the algebraic sum of the moments at the ends of the column (Ma1Mb), divided by its clear height h. In the captive column, due to the presence of a restraining element external to it, the clear height is significantly reduced, increasing the shear force in inverse proportion. To give an idea of the order of magnitude involved, for a typical 2.5-m-story clear height the presence of 2-m-tall nonstructural walls creating a 0.5 m opening in the upper part will form a lateral restriction that will increase fivefold (2.5/0.555) the shear force that the column has to resist as compared to the shear force computed for the column without the nonstructural wall restriction.

The sad lesson, learned again and again in every earthquake, is that the relatively rigid nonstructural element has the power to control the shear force the column must resist! 

If this is the case, the first question that comes to mind is why doesn’t the captivecolumn effect cause problems in the gravity load cases? In reality the problem is there, but since the magnitude of the flexural moments is small, the lateral deflections of the column are also small, and only in extreme cases does the column feel the restriction imposed by the nonstructural wall; the problem is minor, if it exists at all. 

This is not the case under lateral load where the flexural moments are large, the corresponding lateral deflections are also large—mainly because they are controlled by the story drift—and the presence of the nonstructural wall is felt by the column from the onset of the lateral deformation inducing the extremely large shear forces that produce the observed column failures. With regard to reinforced concrete structures subjected to strong earthquake motion effects, one of the premises of modern earthquake resistant design philosophy is to let the structure respond in the nonlinear range at levels well beyond the deformations that will cause yielding of the longitudinal reinforcement of the elements. This response in the inelastic range produces an energy dissipation through flexure that diverts part of the energy that induces vibration in the structure, thus allowing the structure to survive the earthquake motions without having the full strength that would be required if the energy dissipation did not occur. For this dissipation of energy to occur, two fundamental premises must be observed, among others:

• The concrete must be able to accept strains well beyond the values that will cause failure of the material under normal circumstances. This is achieved by ample use of confining transverse reinforcement at critical locations within the structural elements, and 

• The structural element should not fail in shear before the energy dissipation takes place. 

This is achieved by the adequate use of transverse shear reinforcement along the full length of the element. In order to warrant compliance of the second premise, modern earthquake resistant design codes require that the design shear force (Ve) of the element should be obtained from the use of the probable flexural moment strengths (Mpr) at the ends of the element. The probable moment strengths must be obtained, in turn, employing the actual longitudinal reinforcement area at the faces of the element, a yield strength for the reinforcing steel equivalent to 1.25 times the nominal yield strength, and a strength reduction factor (f) equal to one. The design shear force (Ve) is then obtained using Equation 1 and the appropriate values, as described in Equation 2: 

The above-described procedure tries to avoid the existence of structural elements that would fail in shear before reaching the capacity to dissipate energy in flexure. Unfortunately, the existence of captive columns caused by nonstructural elements not taken into account by the structural engineer when applying Equation 2 defeats the whole purpose of this procedure. The value of h to be employed in Equation 2 must be consistent with the actual deformation restraints applied by the structural and nonstructural elements. Now, turning our attention to the captive-column cases described previously where horizontal structural elements frame into the column at mid-height or columns are made shorter by sloping ground, the same principles just described can be employed. 

The flexural stiffness of a column is inversely proportional to its clear height. As the clear height is halved (in reality it is made even less than half due to the depth of the horizontal framing element), the lateral stiffness of the column increases in inverse proportion. When the lateral force story shear is distributed to all columns in the same floor, shorter columns will be called upon to resist a larger portion of the story shear than normal height columns. Although most frame-analysis procedures detect this shear difference, the shear strength required for the column responding in the nonlinear range must be determined from the probable flexural strength at the ends of the column as described by Equation 2. This means that the shear forces obtained from analysis have no relation whatsoever to the required shear strength, and if the shear design of the column is made using the analysis results, the shorter portion of the captive column will be extremely vulnerable under earthquake motions. 

This vulnerability exists in all captive columns designed under codes enacted before the shear-related-to-flexural-strength requirement was introduced. The fact that the shear strength of the element should be computed from the flexural strength at its ends was first proposed by Blume et al. (1961). It was introduced in Appendix A of the ACI-318 code in the 1971 issue (ACI Comm. 318 1971) and was adopted by the Uniform Building Code in 1973 (ICBO 1973). Based on this, any captive column designed and built before the mid 1970s would be suspect of being vulnerable in shear, and this explains the disproportionate number of cases of captive-column failures observed during earthquakes in old buildings and structures not built following modern seismic codes. This situation can also be present even in more recent structures built following modern codes, where interaction with nonstructural elements was not taken into account in design or when stiff nonstructural elements are introduced by the owner or occupant without assessing its potential harmful effect. 


The number of experimental research projects on short and captive columns does not correspond to the number of times the problem is observed in the field during earthquakes and to how widespread the problem is in general. The reason behind this is related to the fact that actual solutions from the structural point of view are of dubious effectiveness and the general approach has always been to term it as an architectural problem that can be solved through proper education of the architectural community at large. Nevertheless, before trying to propose solutions that only highlight the ‘‘interface’’ root of the matter, it is important to have a feeling of the behavior of the short and captive column as observed in experimental tests. Two research programs are worth describing within this context. The authors make no claim of giving an exhaustive listing of all the published research on the problem, and describe the following experimental programs solely as paths toward finding an understanding of the problem. 

Tests at the University of Texas at Austin 

During the 1980s at the University of Texas at Austin, a series of experimental research programs designed to establish the parameters that control the behavior of structural short columns were conducted. The aim of the research project was to establish design parameters that could warrant an appropriate behavior of the column when subjected to earthquake imposed loads. The experimental program and the main conclusions obtained are described in Mayurama et al. (1984), Umehara and Jirsa (1984), and Woodward and Jirsa (1984). Several short columns were tested under imposed lateral cyclic deformations. The main conclusions that can be derived from this experimental program are as follows: 

• When the behavior of short columns with no axial load were compared with short columns with axial loads below the balanced axial load, it was found that the axial load increased the stiffness and the lateral load strength of the column. On the other hand, this axial load increased the strength degradation for cyclic loading once the maximum lateral load resistance was reached. 

• When comparing cyclic test with monotonic tests, the strength of the column under cyclic loads decreased once the maximum lateral load resistance was reached. 

• When comparing columns with different transverse reinforcing spacing (65 to 300 mm), shear strength was found to be insensitive to the transverse reinforcement spacing and depended solely on the shear strength of the concrete alone. This factor, by itself, could explain the brittleness of these elements during earthquakes. 

• It was practically impossible to obtain a stable flexural inelastic response of the columns, and all of them exhibited hysteretic unstable responses. Columns with less longitudinal reinforcements exhibited a better response than those with greater longitudinal reinforcing ratios. 

The results of this research project show that short-column construction should be avoided at all costs, and that any effort in trying to solve the problem by additional transverse reinforcement is not warranted, just confirming the fact that the solution is to avoid the captive column or short column, not to try to tame it.

A confirmation of the findings at the University of Texas had been observed during the 12 June 1978 Miyagi-ken Oki earthquake in Japan. Nonstructural but monolithically cast concrete walls restrained the deformation of a slender reinforced concrete column and caused the lateral deformation to concentrate in a short length as shown in Figure 22. The column had transverse reinforcement as required by the then current code. 

Test at the Universidad de los Andes at Bogota, Colombia 

In 1994 J. C. Pineda performed experimental tests, at the Structures Laboratory of the Universidad de los Andes in Bogotá, Colombia, trying to reproduce captive-column failures in 1:3 scale models (Pineda 1994). In total, three models were tested. Figure 23 shows the captive-column failure observed in Model 1. The other two models were used to test captive-column solution schemes. 

The solution schemes were aimed at finding solutions from the nonstructural element point of view by adding wall elements that would close the opening near the column, as shown in Figure 24. Figure 25 shows the final state of cracking for model 2.

The conclusions of the project indicated a way to avoid captive-column failures only for those cases where the frame containing the captive column is able to control the lateral deformations of the whole structure. The proposed solution was simply defending the column with the addition of masonry inserts at both sides of the column, closing the gap that causes the captive-column effect and allowing the compression strut in the masonry wall to travel along the masonry wall plane, thus diverting away the critical shear force from the reinforced concrete column. 

The proposed recommendation derived from these concepts was to add masonry inserts with a horizontal length of twice the gap opening that produces the captive-column problem, with the masonry covering the whole height of the column. It was also recommended that the wall should be checked for the imposed loads to guarantee that it will not fail along the compression strut, and the columns should be able to resist the forces imposed by the strut at the corners of the panel.


Historically, the more damaging effect of interaction of reinforced concrete frames with nonstructural elements has been the captive-column effect. This type of wall arrangement is common in educational buildings or other buildings where the window is provided for lighting/ventilation purposes only. This situation introduces large shear stresses, when the structure is subjected to lateral forces that are not accounted for in the standard frame design procedures. 

The best solution for captive columns is to avoid the problem. Any type of nonstructural element that could hinder the free deformation capacity of a vertical structural element should be located in a different acting plane than the structural element, or must be separated from the structural element by appropriate joints. When the isolation option is adopted, the designer should guarantee the out-of-plane lateral stability of the wall. For split-level buildings, in order to circumvent the short-column effect, the architect should avoid locating a frame at the vertical plane where the transition between levels occurs. For buildings on slopes, special care should be exercised to locate the sloping retaining walls in such a way that no captive-column effects are induced. 

Where stiff nonstructural walls are still employed, these walls should be separated from the structure, and in no case can they be interrupted before reaching the full height of the adjoining columns. The architect must study carefully the use of nonstructural components in order to avoid unwelcome interaction with the structure of the building. The structural designer should address the influence of masonry infill walls in the lateral force behavior of the structure, either by taking them into account in the design process or by a separation gap from the column. If a separation gap is provided, then appropriate measures should be taken to warrant the out-of-plane stability of the masonry when subjected to lateral forces from wind or earthquake. 

The requirements for obtaining a remodeling permit from a construction authority should provide prescriptions for the owner, the architect, and the contractor on what to do when a captive-column effect is present in a project for remodeling a building. The ‘‘Essential Requirements for Reinforced Concrete Buildings’’ document (ACI et al. 2002) developed under an agreement between the American Concrete Institute, the Colombian Institute for Technical Standards and Certification, and the Colombian Association for Earthquake Engineering provides some recommendations regarding the two alternative corrective measures discussed.

L. Teresa Guevara. M. EERI. Director, Proyectos V&G Consulting Architects, Caracas, Venezuela. Guest Associate Profesor, Facultad de Arquitectura y Urbanismo, Universidad Central de Venezuela (FAU-UCV). email:

Luis E. García. M. EERI. Professor of Civil Engineering, Universidad de los Andes, Bogotá, Colombia. Partner, Proyectos y Diseños Ltda. Consulting Engineers, Bogotá, Colombia. email:


[1] Guevara, L. T., (1989), Architectural considerations in the design of earthquake-resistant buildings: influence of floor-plan shape on the response of medium-rise housing to earthquake. Ph.D. in Architecture Dissertation. Berkeley: Graduate Division, University of California, Berkeley, p. 38. 

[2] García, Luis E., (1991), Columnas de concreto reforzado, (in Spanish), Universidad de los Andes, Serie Selecta de Asocreto, Bogotá, Colombia, p. 192. (In Spanish.) 

[3] Asociación Colombiana de Ingeniería Sísmica (AIS), (1998), Normas colombianas de diseño y construcción sismo resistente - NSR-98 (Ley 400 de 1997 y Decreto 33 de 1998) , (in Spanish), Bogotá, Colombia, 2 Vol. (In Spanish.) 

[4] Blume, J. A., N. M. Newmark, and L. H. Corning, (1961), Design of Multistory Reinforced Concrete Buildings for Earthquake Motions, Portland Cement Association, Skokie, IL, 318 p. 

[5] Committee 318, (1971), Building Code Requirements for Reinforced Concrete (ACI 318-71), American Concrete Institute, Detroit, MI, 102 p. 

[6] International Conference of Building Officials, (1973), Uniform Building Code (UBC-73), ICBO, Whittier, CA, 704 p. 

[7] Mayurama, K., H. Ramírez, and J. Jirsa, (1984), Short reinforced concrete columns under bilateral load histories, Journal of Structural Engineering, Vol. 110, 1, American Society of Civil Engineers, January, pp. 120-137. 

[8] Umehara, H., and J. Jirsa, (1984), Short rectangular reinforced concrete columns under bi-directional loading, Journal of Structural Engineering, Vol. 110, 3, American Society of Civil Engineers, March, pp. 605-618. 

[9] Woodward, K., and J. Jirsa, (1984), Influence of reinforcement on reinforced concrete short column lateral resistance, Journal of Structural Engineering, Vol. 110, 1, American Society of Civil Engineers, January, pp. 90-104. 

[10] Pineda, J. C., (1995), Ensayos experimentales sobre control de columnas cortas, (in Spanish), Proyecto de Grado IC-94-II-26, Advisor: L. E. García, Departamento de Ingeniería Civil, Universidad de los Andes, Bogotá, 43 p. (In Spanish.) 

[11] American Concrete Institute - ACI, Instituto Colombiano de Normas Técnicas y Certificación - Icontec, and Asociación Colombiana de Ingeniería Sísmica - AIS, (2002), Essential Requirements for Reinforced Concrete Buildings, International Publication Series 1, American Concrete Institute, Farmington Hills, MI, 246 p. 

[12] Guevara, L. T. and L. E. García, (1999), La columna corta o columna cautiva, (in Spanish), Revista Noticreto, 52, Asociación Colombiana de Productores de Concreto – Asocreto, julio-septiembre, Bogotá, pp. 46-54. (In Spanish.)