**6. The structural health monitoring of the Basilica di Collemaggio**

The Basilica S. Maria di Collemaggio is one of the most attractive churches in Centre Italy. It dates from the XV century. The Basilica has a nave and two side aisles. The dimension of the nave is 61m in length and 11.3m in width; its height reaches 18.25m. The two side aisles are 7.8 and 8m in width; two external walls both 12.5m high delimit them. Seven columns, not evenly distanced, on each side separate the nave and two side aisles. The columns are about 5.25m high; a layer of well-laid stone, made of a calcareous material arranged irregularly in a poor quality mortar, encloses their core; the transverse section, approximately circular, is on average 1.00 m in diameter. The thickness of masonry varies from 0.95 m to 1.05 in the external walls; it is 0.9m in the two walls of the nave, over the columns. The four walls are connected on one side to the facade of the Basilica and, on the other side, to the transept. The facade is joined to a thick octagonal tower on the right corner; another masonry building is adjacent to a part of the wall, about 40% of it, behind the tower. The wooden roof is supported from trusses placed in a cross-sectional direction to the walls.

the sensor nodes to a central gateway connected to a PC that performs the entire processing. However, modern sensor nodes are equipped with a microprocessor, allowing them to carry out local processing of data. In other words, data processing can be distributed across the

The wireless systems, in fact, have progressed very rapidly in recent years and are now considered the enabling technology for realizing the pervasive ubiquitous computing envi‐ ronment that should support advanced distributed applications in many domains, especially

Therefore, owing to unprecedented design challenges and potentially large revenues, wireless sensor networks are calling huge interest in both the scientific and the industrial world. Besides a secure optimization of transmission (as shown by ISHMP work, whose software is already partially decentralized), processing de-centralization can bring the advantage of being able to quickly detect local phenomena, even in case of network splitting as a consequence of critical phenomena as an earthquake. This capability can be extremely useful insecurity systems or,

A series of activities are still under development to rethink structural modal analysis techni‐ ques, towards the goal of a distributed processing within the network, which could efficiently support real-time monitoring and safety oriented services [10]. Firstly, moving from the achievements and contributions of ISHMP, an iMote2-based monitoring system was devel‐ oped. Moreover, the ISHMP software tools will be integrated with ad-hoc applications, in order to achieve an efficient distributed processing within our network. Moreover, optimizations of limited energy resources may be achieved through suited techniques of data compression and aggregation, providing reduced energy costs of communications and lower channel capacity

The choice of the ISHMP software tools is not simply determined by the convenience of having a ready-to-use, decentralized-oriented middleware, but has a deeper reason. In fact, given the particular characteristics of the processing, the ISHMP Toolsuite was designed as a servicebased software architecture. In other words, the various processing steps are implemented as

The Basilica S. Maria di Collemaggio is one of the most attractive churches in Centre Italy. It dates from the XV century. The Basilica has a nave and two side aisles. The dimension of the nave is 61m in length and 11.3m in width; its height reaches 18.25m. The two side aisles are 7.8 and 8m in width; two external walls both 12.5m high delimit them. Seven columns, not evenly distanced, on each side separate the nave and two side aisles. The columns are about 5.25m high; a layer of well-laid stone, made of a calcareous material arranged irregularly in a poor quality mortar, encloses their core; the transverse section, approximately circular, is on average 1.00 m in diameter. The thickness of masonry varies from 0.95 m to 1.05 in the external

services, and each application is just a collection of independent modules.

**6. The structural health monitoring of the Basilica di Collemaggio**

network.

for data delivery.

for advanced distributed applications.

generally, in the field of emergency management.

228 Engineering Seismology, Geotechnical and Structural Earthquake Engineering

Before the occurring of the 6th April 2009 earthquake a numerical and experimental study has permitted to characterize the dynamic behavior of the Basilica [32-34]. The experimental data were firstly used to identify a modal model and then to determine suitable FE models able to predict and frame the dynamical response of the church. Preliminary numerical analyses were carried out on the basis of several assumptions regarding: (1) mechanical parameters of masonry, (2) timber trusses of the roof, (3) restraints in walls and columns, (4) links among structural components. Afterwards the Basilica was excited at a low level by an instrumented hammer and a mechanical vibration exciter (vibrodyne). Several tests have been carried out, with different positions of the instruments and impact locations, in order to excite and to measure as many modes as possible.

The vibrodyne was located on the top of a lateral wall. The frequency responses were directly measured around the first two modes; these are the most important ones that describe the dynamic response of the church. Experimental data have been used to identify natural

**Figure 11.** Drawings for the locations of the 16 smart sensors mounting tri-axial MEMS accelerometers, humidity and temperature measuring instruments, installed at the Basilica di S. Maria di Collemaggio, at L'Aquila, Italy.

frequencies, modal displacements and damping factors. The first campaign of tests [32] have permitted to recognise at least four major resonance peaks in the range 0.8÷3.0 Hz.

modes of this element are in a frequency range higher than the transversal mode of the nave. Recently, after the earthquake a strong effort has been made to use all the available data from the previous on-site dynamic campaign in order to develop a series of complete finite element models of the Basilica able to reproduce the main modal identified characteristics and the collapse scenario [35]. Starting from these models, a reproduction of the scenario after the collapse has been pursued [8, 36]. A campaign of numerical simulations has been conducted to evaluate the dynamic response of the Basilica together with the temporary retrofitting under

Advanced Applications in the Field of Structural Control and Health Monitoring After the 2009 L'Aquila Earthquake

The previous installation for the on-site dynamic testing campaigns together with the obser‐ vation obtained by the modelling have driven the monitoring installation scheme reported in Figure 11. The wireless network composed by 16 smart sensors (see also Table 3) has been finally installed on June 2011. During the successive months the monitoring system has been enhanced and brought to complete and automatic management to sense seismic induced vibrations. During this path, several test campaigns have been conducted making use of different induced source of vibrations such as hammer, ambient vibrations and free-vibration tests [37]. Finally, in six cases, the seismic induced response of the structures of S. Maria di Collemaggio has been cleared measured, as reported in Table 5. The results of the identification

 Main shock Emilia 20/05/2012 2.03 5,9 0,0054 Aftershock Emilia 20/05/2012 13.18 5,1 0,0018 Shock Ravenna 06/06/2012 6.08 4,5 0,0014 L'Aquila 14/10/2012 16.32 2,8 0,0072 L'Aquila 30/10/2012 2.52 3,6 0,0073 L'Aquila 16/11/2012 3.37 3,2 0,0082

**MI Number Maximum recorded** 

The chapter aims to present the rapid development in the transfer to the real applications of the available technology in the sector of structural control and health monitoring, occurred at L'Aquila immediately after the 2009, L'Aquila earthquake. The benefits in the application of these emerging technologies are still under verification and observation. For the performance evaluation of the installed seismic protections systems, only the occurrence of a relative strong seismic motion, will clearly evidence the benefits introduced in the territory. Differently, the large amount of activities concerning material and in-situ testing together with small or longterm monitoring will surely increment the knowledge regarding the real behaviour of complex masonry or reinforce concrete structures. The amount of obtained data from this large campaign of testing, conducted with different techniques and aims, is in many cases larger

**UTC**

**Magnitudo** 

**response acceleration (g)**

http://dx.doi.org/10.5772/55438

231

**Earthquakes Date Time** 

small earthquakes characterizing the numerous aftershocks at L'Aquila.

process will be object of further publications.

**Table 6.** Recorded structural response of S. Maria di Collemaggio.

**7. Conclusions**

The first two peaks are around frequencies values, about 1.25 and 1.7 Hz. Other peaks are present over 2 Hz. Two of them, around 2.5 and 2.7 Hz, are well defined in all tests. Secondary peaks, around 2.2, 2.3 and 2.6 Hz, are not always visible in all the responses; they indicate the occurrence of highly coupled modes. These peaks, however, are estimated to be less important: numerical analysis indicates that the participating mass of first two modes is at least 85% of total mass in the transverse direction of the church.

After retrofitting, all peaks are shifted to higher frequencies [33]. The first two are around 1.45 Hz and 2.12 Hz respectively. Other peaks are clearly visible around 2.6 and 2.95 Hz. Secondary peaks, which are not always visible in all the responses, are recognisable even in this case. Higher frequencies are a consequence of the increasing stiffness brought about by retrofitting. It is interesting to observe that now the responses of a pair of accelerometers are basically identical, at least in the range of frequencies examined. This is a clear indication that the retrofitting had improved the link between the longitudinal walls. Other dynamic testing have been performed on the facade [34] which have permitted to evidence that out-of-plane local

**Figure 12.** Installation phases of the monitoring system at the Basilica di S. Maria di Collemaggio: a) b) sensor posi‐ tioning on the central walls of the nave, c) sensor positioning beyond the facade, d) f) sensor views, g) phase of on-site testing, h) sensor positioning at the end of the nave walls.

modes of this element are in a frequency range higher than the transversal mode of the nave. Recently, after the earthquake a strong effort has been made to use all the available data from the previous on-site dynamic campaign in order to develop a series of complete finite element models of the Basilica able to reproduce the main modal identified characteristics and the collapse scenario [35]. Starting from these models, a reproduction of the scenario after the collapse has been pursued [8, 36]. A campaign of numerical simulations has been conducted to evaluate the dynamic response of the Basilica together with the temporary retrofitting under small earthquakes characterizing the numerous aftershocks at L'Aquila.

The previous installation for the on-site dynamic testing campaigns together with the obser‐ vation obtained by the modelling have driven the monitoring installation scheme reported in Figure 11. The wireless network composed by 16 smart sensors (see also Table 3) has been finally installed on June 2011. During the successive months the monitoring system has been enhanced and brought to complete and automatic management to sense seismic induced vibrations. During this path, several test campaigns have been conducted making use of different induced source of vibrations such as hammer, ambient vibrations and free-vibration tests [37]. Finally, in six cases, the seismic induced response of the structures of S. Maria di Collemaggio has been cleared measured, as reported in Table 5. The results of the identification process will be object of further publications.


**Table 6.** Recorded structural response of S. Maria di Collemaggio.
