# A Review of Blast Loading in the Urban Environment
## 2 Current Knowledge
### Effects of Street Confinement  
[PERSON] et al. (2014) explored blast wave propagation within modelled street environments. Specific layouts selected for testing include a straight street, a T-junction and a cross junction. An explosive bridge wire detonator, type RP80, was used to create equivalent, small-scale free air blasts. It was seen that an increase in overpressure persists out to greater distances when the confinement of a street is present, compared to a free-air scenario; similar findings were reported by [PERSON] et al. (2017). However, the increase in overpressure is not seen at shorter-scaled distances. Instead, it is seen to be similar to the overpressure experienced in a free-field scenario. Figure 3 shows a sample of these results and is also supplemented with additional reference curves from free-field hemispherical TNT surface blast tests from [PERSON] and [PERSON] (2014) and France groupe d'etude des Modes Operatoires (GEMO) ([PERSON] and [PERSON] 2015). This behaviour is described as a result of the reflected shock wave not yet merging with the incident shock wave. Instead, a pressure sensor reads two peaks, where the amplitude is similar to that of a free-field blast. Therefore, the scaled impulse was used to quantify blast loading at smaller-scaled distances within wider street widths. In addition to the street width and shape, the confining building height was also considered. It was found that the height of the buildings also alters the blast characteristics. In the case of a tall street, the blast parameters are enhanced as the blast's energy is more contained. A taller street will consistently experience larger pressures and scaled impulses compared to a shorter street of the same width and shape. Channelling effects through an array of buildings were also explored; the array sizing was 4 \(\times\) 4 and slightly rectangular (skewed in the longitudinal direction). It is stated that _\"between the spaced buildings that decrease the blast characteristics and the confinement that increases them, the blast characteristics are similar to a free-field propagation\"_. Whilst this statement is made, closer inspection reveals that impulse data within the array is slightly reduced compared to free-field data. This could be linked to the behaviour characteristics of shielding and channelling \"somewhat mitigating\" each other in [PERSON] et al. (2017), but overall resulting in a small reduction of impulse. However, it is seen that once the blast exits the array, the pressure and impulse experience an 80% reduction compared to a free-field scenario. This could suggest that global energy loss of the shock wave occurs as it propagates through an array, but the confining effect of the array largely compensates for this energy loss. It is only when a shock wave propagates beyond an array that the energy loss is significantly shown in the reduction of the pressure and impulse. [PERSON] and [PERSON] (2017) numerically and experimentally investigated blasts within straight streets. Model streets were constructed out of concrete blocks and beams that formed a set of parallel walls. The walls acted as building facades where multiple pressure transducers were installed. Initially, experimental and numerical results showed good agreement, validating the use of Air3D for the remainder of the study. The numerical investigation found that the smaller street widths and taller building heights increased the positive phase impulse for the same explosive mass. It was also found that a scaled street width of 4.8 m/kg\({}^{1/3}\) can be considered the limit where reflections from one side of the street do not affect the loading on buildings at the other side of the street. Additionally, in observations that were later ratified by [PERSON] et al. [42], it was seen that larger building heights also increased the scaled impulse for the same explosive mass. A building height of 3.2 m/kg\({}^{1/3}\) or greater can be considered \"infinitely tall\".