**1. Introduction**

Precast concrete construction represents a very important percentage of all civil works in the world, given its enormous advantages from a constructive point of view. The reduction of the manufacturing time, the improvement in the quality of the work (due to the improvement of the working conditions), and the reduction of uncertainties related to the geometric and structural deviation of the solution with respect to the project are some of the advantages of this constructive procedure.

Precast concrete is especially e fficient in residential structures, which are generally made up of a few groups of di fferent structural elements (columns, slabs, footings, walls, etc.), formed by many identical units. In particular, precast concrete is especially interesting in developing countries, where it can be di fficult to find enough skilled labour to perform in situ constructions.

A significant number of these developing countries are in areas of high seismic activity. This is an inconvenience for precast solutions, since it is penalized by international regulations by granting lower reduction coe fficients (R) for energy dissipation. This is due to the lower ductility of the connections

between elements, that is, the limitation is not due to the precast element by itself, but due to the connections between them, which are usually less ductile than traditional solutions cast in situ.

In these cases, the usual way to address the seismic problem is through the use of seismic isolators, dampers, energy dissipators, etc. However, most of them are very expensive solutions, only suitable for special structural elements (tall buildings or very singular buildings). Therefore, they are not economically viable if massive use is intended in areas with low economic resources [1–8].

Therefore, it is necessary to develop low-cost energy dissipation systems that are capable of being implemented in inexpensive precast concrete buildings without involving an unacceptable increase in the total cost of the building [9–11].

Another common problem regarding the structural behavior of a building that had been subjected to an earthquake was that it was useless after the seismic event and, therefore, it had to be demolished. Regarding the situation of collapse during an earthquake, although it is a breakthrough, the economic cost for the community is still very high. Consequently, it is highly desirable that low-cost energy dissipation systems prevent damage to the structure, and therefore it can be re-occupied under safe conditions once the seismic event has passed.

Research in seismic response of structures, especially if they are made of concrete, requires tests that are usually complex and expensive. On the one hand, the performance of scale tests of concrete structural elements is usually not a viable or reliable option. On the other hand, conducting seismic tests usually requires expensive facilities. Therefore, alternative methodologies have been developed which are easier to implement and obtain, although partially, information on the seismic response of the structure [12,13].

First, there are the quasi-static or cyclic tests, also called "pushover", which consist of the application of a low number of low frequency cyclic loads with increasing amplitude until collapse. This type of test characterizes the ductility of the structure, as well as analyzes very specific regions (connections between elements, singular construction details, etc.) [14–21].

Second, there are pseudo-dynamic tests that are a special type of quasi-static test in which displacements are introduced at some points in the structure. The di fference is that these displacements are not known before the test and are calculated during the test using a step-by-step integration software. Although it is essentially a static test, it is a very complex technique to implement, mainly because a sophisticated adaptive control equipment is required [22–25].

Third, there are the tests carried out on a shake table, which introduce a true dynamic excitation in the base of the structure. This is the most realistic technique for the seismic testing of structures, since the displacements (and therefore, the accelerations) are applied at the base and the structure is subjected to the inertial forces. However, it is a very complex test because of all the equipment required. In addition, its interpretation is also di fficult, since a large number of structural mechanisms are involved in the seismic response. Therefore, this type of tests is usually carried out at the end of a much more extensive testing campaign [26–33].

This paper shows the design and the laboratory validation tests for a new low-cost energy dissipation system that can be applied in precast concrete structures composed of precast footings, precast structural walls and precast concrete slabs. This energy dissipation system basically consists of a specific connection between the precast footing and the precast structural wall, formed by a set of threaded steel bars that connect both elements. During an earthquake, the steel bars undergo plastic deformation, absorbing most of the energy generated by the earthquake and preventing damage to the rest of the building. The additional advantage of this solution is that steel bars are easily replaced after the seismic event.

For the purpose of this paper, a testing campaign was carried out, based on three phases. First, pushover tests were carried out on isolated structural walls formed by a precast structural wall and a precast footing. The aim of this first phase is to define the ductility of the dissipation system, in accordance with the requirements of the American standard ACI 374.2R-13 [34].

Secondly, pushover tests were carried out on structural frames, composed of two precast structural walls placed over two precast footings and connected with a precast slab. The aim of this second phase is to evaluate the ductility of the system, including the dissipation capacity of both the connection footing wall and the connection wall slab, in accordance with the aforementioned regulation.

Thirdly, seismic tests using a shake table were carried out on a real-scale three-storey precast concrete building, consisting of two precast structural walls placed over two precast footings, two intermediate precast slabs, and a lightweight roof. In this case, the aim of this third phase is to characterize the dynamic response of the entire structure to a reference earthquake and the energy dissipation capacity of the building.

A customized unidirectional shake table was designed and manufactured specifically for the third test phase. This testing facility was capable of appling a horizontal acceleration up to 1·g to the structural elements with a height up to 6 m, a weight up to 40 tons, and a frequency up to 8 Hz.

All the precast concrete elements, as well as the low-cost energy dissipation system were invented, developed, and designed by the Spanish company ICONKRETE 2012, S.L., and therefore this company is the owner of this structural solution and the testing results. The precast elements were manufactured by the company ZENET in its factory in Escalonilla (Toledo, Spain). The test was carried out in the Laboratory of Large Structures of the University of Burgos (Burgos, Spain).

The structure of this paper is as follows: In Section 2, the experimental program is presented; in Section 3, the results of the tests are described and discussed; and finally, in Section 4, the conclusions are shown.
