İnşaat Yük. Müh. Cem Ercan
Emülzer Project and Technical Sales Manager
An earthquake, 5,7 magnitude and 11,9 km underground, occurred at 13:59:24 hours on 26.09.2019 on offshore of Silivri, Istanbul (Marmara Sea). The recent earthquake, the second greatest after 1999 Marmara Earthquake, turned our attentions once again to the sturdiness of the venues we live in. Why are Marmara Earthquake and Istanbul so important?
Because of my profession, I visit many cities of our country. During such visits, I face with reproaches such as “Everything is done and provided to Istanbul; why Istanbul is so important?” Although my family is of Elazığ origin, we live in Istanbul for about 80 years. We are of Istanbul origin, now.
Based on the 2017 Activity Report of Revenue Administration, 760,214 billion TRY of tax liability was accrued in the previous year across the country, including those carried over from previous years. Out of this sum, 625,512 billion TRY is collected.
For Istanbul;
Accrual: 326,234 billion TRY
Collection: 275,34 billion TRY
Collection Ratio: 84,40 percent.
The ratio was 44,4 percent in total accrued amount.
That is why Istanbul is extremely important. Nevertheless, in comparison to the taxes collected therefrom, the ratio of what Istanbul gets from Turkish budget is lower. Under the circumstances, it is possible to say that the investments made in and to Istanbul are much less. Development of Istanbul to such great extent is technically not very good. If such anticipated Marmara earthquake with a magnitude of 7 or over occurs, there will be great number of deaths besides material damages. There is a critical risk for our country. Horizontal housing structuring must be started urgently, and an expansion must be ensured starting from neighboring provinces.
What determines the skeleton of a reinforced concrete building is iron and concrete. Producers of iron are known; therefore, it is possible to carry out inspections before iron goes into molds. Nevertheless, the situation for ready concrete is not the same; because it is not all ready. It is prepared and dispatched upon purchase orders. Therefore, concrete must be kept under control very well from its fresh form until hardened state. We have sufficient number of laws, standards, and regulations on concrete design. Ready-concrete facilities are highly sophisticated and accordingly, error margin is minimized in mechanical production. Nevertheless, comprised of cement, water, agrega (sand, rock dust, crushed stone-1 (5-12), crushed stone-2 (12-20)), chemical additives, mineral additives, in short 8 components, concrete production unfortunately cannot be inspected; because there is human factor in its every stage. Different individuals perform ready-concrete preparation and pouring it into molds. As is the case in developed countries and done by some domestic ready-concrete producers, ready-concrete companies must pour concrete into forms and cure it. Consequently, human factors in each stage will be eliminated. Subcontractors must form an organization under ready-concrete companies. It is obvious that this will be applied widespread in future.
There are revisions made to Law on Construction Inspections. Accordingly, inspections via chipped concrete specimens became essential and requirement for concrete laboratories. It is a highly sound decision. However, having fresh concrete designed perfectly is not enough; it is also essential that pouring it in place and subsequent curing processes must be in recommended standards.
Approaches such as getting away with mistakes, benefiting therefrom by those with economic and political influences, and ill intentions unfortunately cause problems in practice despite having perfect standards, legislations, and regulations in effect. That also has adverse effects on basic income distribution. Only science, ethics, social self-control, and universal laws can solve problems.
The year 2019 was declared as “pedestrian-preferential traffic year”. According to the laws, vehicles are obliged to give the right of way to pedestrians. It is necessary to have social responsibility and awareness popular. For instance, drivers must be cautious for the car in front just in case the later allows pedestrians to cross the road at a pedestrian crossing. Braking distance must be complied, no honking or misbehaviors must be displayed. On the other hand, pedestrians must cross roads only at pedestrian crossings, not anywhere across roads, or jumping over barriers on traffic islands. Informed social self-control will ensure us be more civilized in cleanness, health, education, and human relations.
After these anecdotes, let us examine “what we can do” for our buildings against earthquakes.
A-) Concrete Cover Spacers
Buildings in our country are mostly reinforced concrete. Durability of reinforced concrete depends on iron inside it. In other words, if reinforcements of a reinforced concrete building are damaged and lose it durability due to corrosion, that building will collapse. Better the enfolding of reinforcements by concrete, longer the life of a building. Unfortunately, even concrete cover spacers are decreased in order to have more net area (m2) in buildings. Accordingly, some reinforcements become vulnerable to corrosion. Furthermore, such surfaces are not plastered for the sake of saving space. They are directly applied with gypsum. As result of direct contact of gypsum with concrete, corrosion started in some of new buildings. Even though gross concrete priming is applied on concrete before gypsum, this practice is not applied evenly and homogeneously at every point. On the contrary, gross concrete priming is not applied on many surfaces except the ceiling cladding.
No human live can be valorized in calculation of costs. Therefore, building mold systems must be reexamined. No mold must be used when deformed as result of overuse. Attention must be paid to the types of mold release oil. In conclusion, concrete cover spacers must be applied and their range must be increased. There are many examples of concrete cover spacers in other countries. Using only plastic concrete spacers may be insufficient.
B-) Contiguous buildings
In some contiguous buildings, no space is left between buildings. Due to oscillations during an earthquake, both reinforced concrete frames bump into each other at full speed. As result of such impact, structural cracks are formed. Another damage is occurrence of waterproofing issues. While clearance is none or only 1-2 cm at onset, deviations after an earthquake may reach up to 5-15 cm. Water infiltrating from both facade and top floor causes adverse impact on living comfort. Water infiltration leads to chipping of gypsum, blistered paints, and corrosion on overall building. As result of researches conducted, it is noted that number of disease incidents, such as POPD (Chronic Obstructive Pulmonary Disease), asthma, and bronchitis, are increased.
Such places must be repaired by utilizing bitumen- or polyurethane-based products as if there is a dilatation gap in the structure. Such gaps must NOT be filled with rigid cement-based products. Because any rigid material will be cracked as result of movements during an earthquake.
*NOTE: Cement finish indicated as Item 9 is valid for horizontal surfaces. On vertical surfaces, heat sheathing, etc. must be considered.
C-) Basements
It is necessary to go to indoor parking and basements again. Basement height/ building height ratio should not be more than 1/6. In other words, if basement height is 3 meters, then building height should not be more than 18 meters. If the quality of necessary reinforcement and concrete is chosen correctly in the design stage, this rule may be adjusted.
Basements are generally overlooked since they are not in sight of property owners. Nevertheless, an arbor to be built in yard, color shade of facade, or a tree to be planted may cause greater discussions. Reinforcements of concrete surfaces must not be left uncovered. At some places, instead of applying plaster, lime or gypsum is applied. This practice is highly hazardous. Even if there is no corrosion in the environment, it will start and accelerate corrosion. If there is a crack in reinforced concrete, it must be monitored whether it develops or not. If it is covered it becomes impossible to monitor and determine.
Proper waterproofing must be applied whereon water infiltrates, in other words, in the positive direction. On the basements of detached buildings, waterproofing must be performed by clearing around the outer walls of relevant building. Nevertheless, this practice is not used in consideration of the costs. Basements are statically important. They must be waterproofed, if feasible, from outside, and if not, from inside. Waterproofing from inside is not a very good applications. For, even if you prevent water infiltration to building, you cannot avoid corrosion on reinforcements.
As seen in the photograph, there is a small interception ditch opened up for directing water and its propagation. Nevertheless, such methods will not prevent corrosion on reinforcements within reinforced concrete.
The pan method below is unfortunately the system frequently used. Here, you may gather water at a given location and channel it out; yet, you cannot avoid corrosion on reinforcements.
D-) Hollow-block floors
In no governmental building (in general), hollow-blocks are used in construction. Private sector build their building utilizing hollow-blocks, even on multistory buildings, for the sake of finishing works in a short time. Such blocks are very susceptible to heat besides having no density.
Some issues encountered in such building constructed by utilizing hollowblocks are as follows;
1) They are not appropriate to be used in earthquake regions since they cannot attain a full frame.
2) They should not be used without constructing lift joints.
3) Due to such beams of low rigidity, horizontal drift between floors during earthquake get larger and transfers very high second order moments to columns.
4) Air expands and convects upward as it gets warmer. Any surface, and blocks as well, touched by warm air, produces harmful gases.
5) During a fire, such blocks will immediately catch fire and fire will spread.
6) Ceiling plasters drop down as result of jolts of earthquake, etc. Sometimes, even blocks are detached and drop down. It may cause material damages and even injuries if there are children underneath.
As of 2018, the earthquake regulation (Turkish Building Earthquake Regulations, aka, ‘TBDY’) is amended. Prof. Dr. Mehmet Nuray Aydınoğlu from Boğaziçi University, Kandilli Observatory and Earthquake Research Institute, commented on the limitations vested on the building loadbearing systems with hollow-block floors; it must be found and read.
Mr. Aydınoğlu, shortly in the conclusions; in hollow-block floored buildings with DTS (Earthquake Design Class) = 1,2 and BYS (Building Height Class) ≥ 6, curtain walls at both directions must fulfill the tumbling moment requirement given in Equation (4.3) under 4.3.4.6.
Otherwise, hollow-tile floor system (see Table 3.3 for BYS definition) is,
• (a) not usable for any building when DTS = 1.2 ve BYS ≥ 6 (Hn,max = 17,5 m),
• (b) usable for any building when DTS = 3.4 ve BYS ≥ 7 (Hn,max = 17,5 m),
In Summary,
‘Waterproofing Project’ should be made compulsory. Particularly, corrosions on the buildings close to sea and streambeds harm safety, aesthetic, and economic life of buildings without needing an earthquake. Based on the studies conducted, any building constructed without waterproofing loses 66% of its bearing capacity after 10 years. In other words, while a column of 80×60 cm bears a load of 100 tons, it can bear only 34 tons if not waterproofed, but exposed to corrosion.
Depending on the corrosion on reinforced concrete, rate of corrosion varies on reinforcements. While initial pH value of concrete is 14, it gets lower in time. When concrete’s pH value drops in the range of 5 to 9, accordingly, reinforcements swell and expand by 250 micron/year. It starts chipping off the passivation layer, resulting in lateral stress in concrete. In general, such damages appearing to be vertical cracks have nothing to do with earthquake.
Property owners living in such buildings exposed to corrosion should pursue solution to this condition by developing empathy as a social courtesy. When an earthquake occurs, regardless of varying jolts, those living on the first and eighth floors are subject to the same circumstance. Damages on buildings and severity of quakes may vary for each floor. However, psychology and fear during an earthquake are same and similar. Regardless of which floor they reside, ground or top; property owners must deal with the issues of their building. Waterproofing, corrosion, cracks and damages formed in reinforced concrete are collective responsibility of all property owners.
Sometimes during our site visits, we observe this; Contractor keeps the concrete quality higher because he is going to reside on the top floor. Whereas, if there is corrosion in a construction, if concrete compressive strength in lower floors is low, and if workmanship is not well qualified, the favor he is doing during construction will not give him any advantage.
Predestinarianism of the eastern philosophy is not understood by the western countries. The western countries do not understand the predestination belief of the East. In fact, taking measures in line with the hard science, and then trust in and resign to the Creator is the best way to follow.