## 2 Brief Historical Context of Chilean Construction Regulations
### Construction and Urbanism General Ordinance, OGCU-1940  
As a consequence of the devastating earthquake in Chillan on 24 January 1939, which caused more damage and the highest number of fatalities reported in Chile, the government requested the creation of a technical government commission, which submitted an evaluation of the current ordinance with the damage report, highlighting mistakes and ambiguities, proposing new seismic factors and incorporating the first approach to design using a dynamic method; the commission recommended \"... _reinforced concrete buildings to be calculated in a more rational way (that is, taking into consideration not only the maximum acceleration of earthquakes as established by the Ordinance but also the amplitude and period)_\" [15]. This document is the basis of the main changes related to seismic design and generated a new OGCU that was approved in 1940 [16]. The new OGCU included an adjustment with respect to seismic action, which is now considered a harmonic movement, or followed the use of a static method equivalent to that defined in OGCU-1936, which would subsequently depend on the type and period of a structure. Thus, for structures with the period T\({}_{\text{e}}\) less than 0.4 s, the seismic action was determined using the static method defined in OGCU-1936. If T\({}_{\text{e}}\) was greater than or equal to 0.4 s, \"... _the action of the earthquake will assimilate to a horizontal vibration in any direction, of a simple harmonic movement, with the following characteristics: Acceleration 0.1 g to 0.2 g (g gravitational acceleration); amplitude 4 to 6 cm, period 1 to 2 s... \"_. For this last case, the OGCU-1940 established the possibility of using an approximate method to determine the seismic action, which due to the absence of more precise methods suggests that the government commission utilized such a method [17; 15]; based on this reasoning, the provision is interpreted as a seismic classification method, as listed in Table 3.  
As shown in Table 3, OGCU-1940 removed the parameter for classifying the admissible resistance of the ground, reducing it to a general characterization of the ground without main specifications. This lack of a main decree with respect to the ground could be attributed to the effects of the 1939 earthquake, which was uniformly devastating throughout the whole area of influence. These effects would make it more difficult to refine particular aspects associated with the ground. Considering the limited geomechanics exploration that was conducted during this period, the normative analysis was centred more on the identification of the characteristic seismic wave, temporarily and partially disregarding the influence of the ground. Nevertheless, participants in the government commission suggested that geological aspects were required to continue investigation [15].  
Considering bibliographic antecedents available at the time, the OGCU commission in charge of revision observed that at an international level, prominent investigators concurred, indicating that the evidence of earthquakes, such as those in San Francisco in 1906 or Tokyo in 1923, demonstrated that the destructive aspect of earthquakes was attributed to waves whose periods varied between certain defined limits [17] (p. 87). Therefore, with this assumption, the ordinance adopted a criterion to restrict construction, whose T\({}_{\text{e}}\) period would range between 1.0 and 2.0 s. The simplified method, previously indicated and suggested by OGCU-1940, did not explicitly include factors for other periods, such as for T\({}_{\text{e}}\) between 0.75 and 1.0 s and between 2 and 3 s. Therefore, in Table 3, values of seismic action in these period ranges correspond to an interpretation, based on the report of the commission, to complete the analytical range for an accepted T\({}_{\text{e}}\) in OGCU-1940. The maximum values reported for factors \(\alpha\) and \(\beta\) are extrapolated for different site classes.