**6.2 The hazard of non-structural elements**

The typical design of residential buildings in Lorca is formed by a RC supporting structure (columns and beams) and double-leaf external walls separated by an inner cavity, used as thermal insulation, filled with expanded polystyrene sheets. The internal wall is made of hollow brick, and the external wall of unplastered solid red brick. This external panel was not confined into the RC frame, but externally attached with mortar to the structure, acting rather as cladding or load-bearing wall and not properly as infill wall. In addition, the two brick walls were not tied together with any kind of coupling element, and the lack of plaster, which serves as cohesive mesh and grip for the bricks, provided less resistance to the external face.

The 2011 Lorca earthquake caused nine fatalities due to the fall of these nonstructural elements from façades (**Figure 22**) and the evident cause-effect relationship led to a conclusion that became an axiom: non-structural elements also

#### **Figure 20.**

*Lorca, shear cracks in pre-1968 RC buildings of class C (grade 3). There is apparently no evidence of structural damage, and on the ground floor (left) the columns forming an evident soft story have no sign of tilting. Source: IERD.*

**321**

**Figure 21.**

*Effects of Earthquakes on Buildings in the Ibero-Maghrebian Region*

kill [23]. This damage took place in several steps: (1) formation of shear cracks in the infill walls caused by cyclic reverse movements of the ground due to seismic shaking; (2) detachment and drift of external walls from RC frames; (3) bending and fall of cladding and external walls. **Figure 23** shows the different types of damage here described: shear cracks cause the detachment and loss of stone or marble cladding and the toppling of the outer leaf of the masonry wall, made in this case with hollow bricks (grade 3, class C). After the collapse of the wall, the expanded polystyrene sheets are exposed outside the inner cavity of insulation. The drift between brick infills, with no connecting elements between them, is also clear. However, there are no shear cracks in the cantilever plaster at the top of the building entrance, which proves the high vulnerability of the infill wall design. The same situation occurs in **Figure 24**, at a moment prior to the external wall detachment,

*building caused during the collapse, wedging against the base of the column. Source: IERD.*

*Lorca, complete collapse of RC residential building (grade 5) designed under the earthquake-resistant standard prior to the 2002 standard: (a) the three slabs are completely collapsed without any gap to allow survival; (b) plastic hinges and overturning in the direction of the slope of the street; and (c) plastic hinge in the adjacent* 

The lateral loadings were stronger in ground floors, due to the same widespread and wrong conception of structural design exposed in the case of Al Hoceima: the

appearing X-shaped cracks by reversal of shear forces.

*DOI: http://dx.doi.org/10.5772/intechopen.94739*

*Effects of Earthquakes on Buildings in the Ibero-Maghrebian Region DOI: http://dx.doi.org/10.5772/intechopen.94739*

#### **Figure 21.**

*Natural Hazards - Impacts, Adjustments and Resilience*

implies improving resistance.

**6.2 The hazard of non-structural elements**

In Lorca, most of the damaged RC housing blocks had been built in three different construction periods: before the first anti-seismic standard of 1968, during the period from 1968 to 2002, and after 2002 standard, in use on the date of this earthquake. But none of these technical rules devoted enough extension to deal with the coupling conditions of non-structural elements, with the consequences that will be discussed below. The first RC housing blocks in Lorca began to be built from the early 1950s onwards, in a period of time marked by the international blockade and economic situation of autarchy (self-production) of the Spanish government after the Second World War. Faced with the impossibility of importing raw materials, steel rebars of low quality and scarce quantity were used for the two essential elements of RC frames: beams and columns. In fact, several patents were developed

in Spain to create RC beams containing up to only two steel rebars [22].

However, although it seems difficult to explain, older RC buildings did not suffer a greater damage than those built after the 2002 standard. In **Figure 20** we can appreciate slight shear cracks in the façade of pre-1968 RC buildings, not showing apparent structural damage or deformations of RC frames on the ground floor, despite the lower stiffness due to the lack of infill walls (grade 3, class C). Paradoxically, in **Figure 21** we have the complete collapse of the four-story residential block mentioned above, built during the transition period to the 2002 earthquake-resistant standard. This means that improving rules does not always

The typical design of residential buildings in Lorca is formed by a RC supporting structure (columns and beams) and double-leaf external walls separated by an inner cavity, used as thermal insulation, filled with expanded polystyrene sheets. The internal wall is made of hollow brick, and the external wall of unplastered solid red brick. This external panel was not confined into the RC frame, but externally attached with mortar to the structure, acting rather as cladding or load-bearing wall and not properly as infill wall. In addition, the two brick walls were not tied together with any kind of coupling element, and the lack of plaster, which serves as cohesive mesh and grip for the bricks, provided less resistance to the external face. The 2011 Lorca earthquake caused nine fatalities due to the fall of these nonstructural elements from façades (**Figure 22**) and the evident cause-effect relationship led to a conclusion that became an axiom: non-structural elements also

*Lorca, shear cracks in pre-1968 RC buildings of class C (grade 3). There is apparently no evidence of structural damage, and on the ground floor (left) the columns forming an evident soft story have no sign of tilting. Source:* 

**320**

*IERD.*

**Figure 20.**

*Lorca, complete collapse of RC residential building (grade 5) designed under the earthquake-resistant standard prior to the 2002 standard: (a) the three slabs are completely collapsed without any gap to allow survival; (b) plastic hinges and overturning in the direction of the slope of the street; and (c) plastic hinge in the adjacent building caused during the collapse, wedging against the base of the column. Source: IERD.*

kill [23]. This damage took place in several steps: (1) formation of shear cracks in the infill walls caused by cyclic reverse movements of the ground due to seismic shaking; (2) detachment and drift of external walls from RC frames; (3) bending and fall of cladding and external walls. **Figure 23** shows the different types of damage here described: shear cracks cause the detachment and loss of stone or marble cladding and the toppling of the outer leaf of the masonry wall, made in this case with hollow bricks (grade 3, class C). After the collapse of the wall, the expanded polystyrene sheets are exposed outside the inner cavity of insulation. The drift between brick infills, with no connecting elements between them, is also clear. However, there are no shear cracks in the cantilever plaster at the top of the building entrance, which proves the high vulnerability of the infill wall design. The same situation occurs in **Figure 24**, at a moment prior to the external wall detachment, appearing X-shaped cracks by reversal of shear forces.

The lateral loadings were stronger in ground floors, due to the same widespread and wrong conception of structural design exposed in the case of Al Hoceima: the

soft story effect. In this construction pattern, the upper floors are more partitioned for residential use than the ground floor, commonly used for open-plan commercial premises, garage, or other purposes. Given this so unbalanced stiffness distribution, the building performs like a rigid block that swings over RC frames of the ground floor, resulting in shear cracks, corner failure, X-shaped or diagonal cracks, partial or complete overturning of infill walls or, in the worst case, plastic hinges that do involve structural damage.

#### **Figure 22.**

*Lorca, debris fallen on vehicles and sidewalk. The center of the street is free of danger. In Lorca, people died while walking or looking for protection near the façades. Source: IERD.*

#### **Figure 23.**

*Lorca, shear cracks caused the detachment and loss of stone cladding and the toppling of the outer leaf of the brickwork wall (grade 3, class C). Source: IERD.*

**323**

construction costs.

*Effects of Earthquakes on Buildings in the Ibero-Maghrebian Region*

*DOI: http://dx.doi.org/10.5772/intechopen.94739*

**6.3 Miscalculations lead to catastrophic results**

**Figure 24.**

*Source: IERD.*

per column in areas with acceleration ≥0.16 g (m/s2

under acceleration values ≥0.12 g.

The only collapsed building in Lorca was designed under the earthquakeresistant standard of 1995. Following the technical requirements of this regulation, the RC frames, columns and beams, were reinforced by four longitudinal steel bars enclosed by vertical stirrups placed at regular intervals, including the column-beam or column-slab joints. In addition, the stirrup ends were bent at 90°, without forming a hook around the longitudinal rebars. In **Figure 25a–c**, each RC column is made up of four longitudinal steel rebars and stirrups with 90° hooks (**Figure 25d**). The 1994 earthquake-resistant standard required four rebars per column in areas with expected gravity acceleration values <0.16 g and eight rebars

*Lorca, loss of stone cladding, fall of window lintel and X-shaped crack on external wall about to fall down.* 

value for the municipality of Lorca was 0.12 g; therefore, the collapsed building studied here, built in 2001, fulfilled the construction requirements at the time. Afterwards, the 2002 standard reduced to 0.12 g the acceleration value needed to force the implementation of eight rebars per column, but it was too late. Obviously, this building ―and many others of similar design― had used inadequate construction parameters that were to be approved the following year, stablishing stricter technical requirements more consequent with the behavior of RC frames

As said above, the effective acceleration value was 0.37 g, that is, three times higher than the value for which the structure had been engineered. With this level of vulnerability, these RC structures, with four rebars per column arranged for maximum accelerations of 0.12 g, would hardly have been able to withstand the effective accelerations of 0.37 g without suffering severe damage. The design miscalculation of RC frames was 2/3 lower than the real value. If initial calculations had been overestimated, the damage would have been considerably reduced; but reinforcing structures with steel material means a significant increase in

Several photographs taken in the affected area show the difficulty of the RC frames in other residential buildings to resist the violence of the horizontal

). The maximum estimated

*Effects of Earthquakes on Buildings in the Ibero-Maghrebian Region DOI: http://dx.doi.org/10.5772/intechopen.94739*

*Natural Hazards - Impacts, Adjustments and Resilience*

involve structural damage.

soft story effect. In this construction pattern, the upper floors are more partitioned for residential use than the ground floor, commonly used for open-plan commercial premises, garage, or other purposes. Given this so unbalanced stiffness distribution, the building performs like a rigid block that swings over RC frames of the ground floor, resulting in shear cracks, corner failure, X-shaped or diagonal cracks, partial or complete overturning of infill walls or, in the worst case, plastic hinges that do

*Lorca, shear cracks caused the detachment and loss of stone cladding and the toppling of the outer leaf of the* 

*Lorca, debris fallen on vehicles and sidewalk. The center of the street is free of danger. In Lorca, people died* 

*while walking or looking for protection near the façades. Source: IERD.*

**322**

**Figure 23.**

**Figure 22.**

*brickwork wall (grade 3, class C). Source: IERD.*

**Figure 24.** *Lorca, loss of stone cladding, fall of window lintel and X-shaped crack on external wall about to fall down. Source: IERD.*

#### **6.3 Miscalculations lead to catastrophic results**

The only collapsed building in Lorca was designed under the earthquakeresistant standard of 1995. Following the technical requirements of this regulation, the RC frames, columns and beams, were reinforced by four longitudinal steel bars enclosed by vertical stirrups placed at regular intervals, including the column-beam or column-slab joints. In addition, the stirrup ends were bent at 90°, without forming a hook around the longitudinal rebars. In **Figure 25a–c**, each RC column is made up of four longitudinal steel rebars and stirrups with 90° hooks (**Figure 25d**). The 1994 earthquake-resistant standard required four rebars per column in areas with expected gravity acceleration values <0.16 g and eight rebars per column in areas with acceleration ≥0.16 g (m/s2 ). The maximum estimated value for the municipality of Lorca was 0.12 g; therefore, the collapsed building studied here, built in 2001, fulfilled the construction requirements at the time. Afterwards, the 2002 standard reduced to 0.12 g the acceleration value needed to force the implementation of eight rebars per column, but it was too late. Obviously, this building ―and many others of similar design― had used inadequate construction parameters that were to be approved the following year, stablishing stricter technical requirements more consequent with the behavior of RC frames under acceleration values ≥0.12 g.

As said above, the effective acceleration value was 0.37 g, that is, three times higher than the value for which the structure had been engineered. With this level of vulnerability, these RC structures, with four rebars per column arranged for maximum accelerations of 0.12 g, would hardly have been able to withstand the effective accelerations of 0.37 g without suffering severe damage. The design miscalculation of RC frames was 2/3 lower than the real value. If initial calculations had been overestimated, the damage would have been considerably reduced; but reinforcing structures with steel material means a significant increase in construction costs.

Several photographs taken in the affected area show the difficulty of the RC frames in other residential buildings to resist the violence of the horizontal

#### **Figure 25.**

*Lorca, details of the RC residential block collapsed in Lorca, showing the four-rebar cores of beams and columns: (a) and (b) show the regular equidistance between the stirrups near the column-beam joints; (c) beam with similar arrangement of rebars; (d) drawing of the four-rebar longitudinal distribution used in this building with stirrup ends bent at 90°; (e) more adequate design for seismic resistance, with eight rebars and stirrup bent at 135°; (f) correct way to reinforce the RC column-beam joints. Source: IERD.*

forces. As an example of better structural behavior, in **Figure 26** we can observe a complete damage in a double-leaf infill wall in a housing block with overturning of internal and external faces, but without apparent cracks in the RC frame and with no signs of plastic hinges or deformation in the column-beam joint (grade 3, class C). On the contrary, in **Figure 27** the loss of cladding allows us to clearly appreciate the occurrence of shear cracks at the base of the column-beam connection of the second floor, implying in all cases a moderate structural damage. It is due to the much more stiffness of the slab, which overloads the column resistance by sending all the energy of horizontal forces to the column base, not reinforced with an adequate seismic-resistant design. This damage, although less frequently, is not exclusive to the column-beam or column-slabs joints and can also occur in the middle body of the column (**Figure 28**), especially in case of short-column effect.

The damage to the column-beam joints of RC frames is consequence of the lack of steel reinforcement at the coupling node. As shown in **Figure 25**, the stirrups have a regular equidistance along the column as in the beam-column joints; as a result, the RC structure plastifies. A greater number of stirrups in the coupling node, progressively reducing the distance between them towards the intersection core, would increase the structure resistance and distribute the displacement energy along the full length of the columns, not transferring all the cyclic reversal of loads to the column-beam joints (**Figure 25f**). In addition, in areas with a moderate to high level of seismicity the stirrups should be anchored to the longitudinal rebars, overlapping 135° hooks [24] to avoid the opening of the closed-loop and

**325**

**Figure 27.**

**Figure 26.**

*Effects of Earthquakes on Buildings in the Ibero-Maghrebian Region*

outward bending of the rebars (**Figure 25e**). The Turkish Earthquake Code 2007 and Indian Standard IS13920-1993 are two examples of the implementation of these

*Lorca, complete overturning of double-leaf wall with overturning of both brickwork faces, but without* 

*Lorca, cracks in the column-beam base suggest the incipient formation of a plastic hinge. The loss of cladding is* 

*due to a hammering effect with the adjacent building. Source: IERD.*

*DOI: http://dx.doi.org/10.5772/intechopen.94739*

earthquake-resistant requirements.

*apparent cracks in the RC frame. Source: IERD.*

outward bending of the rebars (**Figure 25e**). The Turkish Earthquake Code 2007 and Indian Standard IS13920-1993 are two examples of the implementation of these earthquake-resistant requirements.

#### **Figure 26.**

*Natural Hazards - Impacts, Adjustments and Resilience*

forces. As an example of better structural behavior, in **Figure 26** we can observe a complete damage in a double-leaf infill wall in a housing block with overturning of internal and external faces, but without apparent cracks in the RC frame and with no signs of plastic hinges or deformation in the column-beam joint (grade 3, class C). On the contrary, in **Figure 27** the loss of cladding allows us to clearly appreciate the occurrence of shear cracks at the base of the column-beam connection of the second floor, implying in all cases a moderate structural damage. It is due to the much more stiffness of the slab, which overloads the column resistance by sending all the energy of horizontal forces to the column base, not reinforced with an adequate seismic-resistant design. This damage, although less frequently, is not exclusive to the column-beam or column-slabs joints and can also occur in the middle body of the column (**Figure 28**), especially in case of

*Lorca, details of the RC residential block collapsed in Lorca, showing the four-rebar cores of beams and columns: (a) and (b) show the regular equidistance between the stirrups near the column-beam joints; (c) beam with similar arrangement of rebars; (d) drawing of the four-rebar longitudinal distribution used in this building with stirrup ends bent at 90°; (e) more adequate design for seismic resistance, with eight rebars and* 

*stirrup bent at 135°; (f) correct way to reinforce the RC column-beam joints. Source: IERD.*

The damage to the column-beam joints of RC frames is consequence of the lack of steel reinforcement at the coupling node. As shown in **Figure 25**, the stirrups have a regular equidistance along the column as in the beam-column joints; as a result, the RC structure plastifies. A greater number of stirrups in the coupling node, progressively reducing the distance between them towards the intersection core, would increase the structure resistance and distribute the displacement energy along the full length of the columns, not transferring all the cyclic reversal of loads to the column-beam joints (**Figure 25f**). In addition, in areas with a moderate to high level of seismicity the stirrups should be anchored to the longitudinal rebars, overlapping 135° hooks [24] to avoid the opening of the closed-loop and

**324**

short-column effect.

**Figure 25.**

*Lorca, complete overturning of double-leaf wall with overturning of both brickwork faces, but without apparent cracks in the RC frame. Source: IERD.*

#### **Figure 27.**

*Lorca, cracks in the column-beam base suggest the incipient formation of a plastic hinge. The loss of cladding is due to a hammering effect with the adjacent building. Source: IERD.*

#### **Figure 28.**

*Lorca, X-shaped cracks in infill walls and loss of concrete in the middle body of the RC column suggest a soft story effect. Source: IERD.*
